Add ability to disable avatar publishing

Add "/avatar disable" to comply with point "3.5 Publisher Disables
Avatar Publishing" in XEP-0084.

src/command/cmd_defs.c:2416
Add "disable" argument. Reword the "/avatar" command description
so it flows better.

src/command/cmd_ac.c:1101
Add "disable" to the "/avatar" autocomplete dictionary.

src/command/cmd_funcs.c:9277
Split "/avatar" commands into two groups with an if statement; those
with a parameter and those without. "cons_bad_cmd_usage()" is in both
groups, which is messy. "disable" has similar logic to "set", but it
includes a failure message.

src/xmpp/avatar.c:152
"avatar_publishing_disable()" uses the same logic to publish metadata
as in "avatar_set()".

src/xmpp/avatar.c:238
Add a message to inform users when they do not receive an avatar after
using "/avatar get" and "/avatar open". In case of a failure, the user
will be subscribed to future avatar updates as long as they continue
to use their current instance of profanity. Adding
"caps_remove_feature()" after "cons_show()" will unsubscribe the user
from avatar updates and prevent the user from downloading an avatar
unexpectedly hours later without issuing an "/avatar" command.

src/xmpp/stanza.c:2698
The new "disable" function follows the same logic as
"stanza_create_avatar_metadata_publish_iq()".

src/xmpp/avatar.c

@@ -150,6 +150,17 @@ avatar_set(const char* path)
 }
 #endif
 
+gboolean
+avatar_publishing_disable()
+{
+    xmpp_ctx_t* const ctx = connection_get_ctx();
+    xmpp_stanza_t* iq = stanza_disable_avatar_publish_iq(ctx);
+    iq_send_stanza(iq);
+    xmpp_stanza_release(iq);
+
+    return TRUE;
+}
+
 gboolean
 avatar_get_by_nick(const char* nick, gboolean open)
 {
@@ -224,6 +235,9 @@ _avatar_metadata_handler(xmpp_stanza_t* const stanza, void* const userdata)
                         _avatar_request_item_by_id(from, data);
                     }
                 }
+            } else {
+                cons_show("We couldn't get the user's avatar, possibly because they haven't set one or have disabled avatar publishing. "
+                          "During this Profanity session, you will receive future changes to this user's avatar.");
             }
         }
     }

src/xmpp/avatar.h

@@ -45,3 +45,4 @@ gboolean avatar_set(const char* path);
 #endif
 
 #endif
+gboolean avatar_publishing_disable();

src/xmpp/stanza.c

@@ -2697,6 +2697,42 @@ stanza_create_avatar_metadata_publish_iq(xmpp_ctx_t* ctx, const char* img_data,
     return iq;
 }
 
+xmpp_stanza_t*
+stanza_disable_avatar_publish_iq(xmpp_ctx_t* ctx)
+{
+    char* id = connection_create_stanza_id();
+    xmpp_stanza_t* iq = xmpp_iq_new(ctx, STANZA_TYPE_SET, id);
+    free(id);
+    xmpp_stanza_set_attribute(iq, STANZA_ATTR_FROM, connection_get_fulljid());
+
+    xmpp_stanza_t* pubsub = xmpp_stanza_new(ctx);
+    xmpp_stanza_set_name(pubsub, STANZA_NAME_PUBSUB);
+    xmpp_stanza_set_ns(pubsub, STANZA_NS_PUBSUB);
+
+    xmpp_stanza_t* publish = xmpp_stanza_new(ctx);
+    xmpp_stanza_set_name(publish, STANZA_NAME_PUBLISH);
+    xmpp_stanza_set_attribute(publish, STANZA_ATTR_NODE, STANZA_NS_USER_AVATAR_METADATA);
+
+    xmpp_stanza_t* item = xmpp_stanza_new(ctx);
+    xmpp_stanza_set_name(item, STANZA_NAME_ITEM);
+
+    xmpp_stanza_t* metadata = xmpp_stanza_new(ctx);
+    xmpp_stanza_set_name(metadata, STANZA_NAME_METADATA);
+    xmpp_stanza_set_ns(metadata, STANZA_NS_USER_AVATAR_METADATA);
+
+    xmpp_stanza_add_child(item, metadata);
+    xmpp_stanza_add_child(publish, item);
+    xmpp_stanza_add_child(pubsub, publish);
+    xmpp_stanza_add_child(iq, pubsub);
+
+    xmpp_stanza_release(metadata);
+    xmpp_stanza_release(item);
+    xmpp_stanza_release(publish);
+    xmpp_stanza_release(pubsub);
+
+    return iq;
+}
+
 xmpp_stanza_t*
 stanza_create_vcard_request_iq(xmpp_ctx_t* ctx, const char* const jid, const char* const stanza_id)
 {

src/xmpp/stanza.h

@@ -418,6 +418,7 @@ void stanza_free_caps(XMPPCaps* caps);
 xmpp_stanza_t* stanza_create_avatar_retrieve_data_request(xmpp_ctx_t* ctx, const char* stanza_id, const char* const item_id, const char* const jid);
 xmpp_stanza_t* stanza_create_avatar_data_publish_iq(xmpp_ctx_t* ctx, const char* img_data, gsize len);
 xmpp_stanza_t* stanza_create_avatar_metadata_publish_iq(xmpp_ctx_t* ctx, const char* img_data, gsize len, int height, int width);
+xmpp_stanza_t* stanza_disable_avatar_publish_iq(xmpp_ctx_t* ctx);
 xmpp_stanza_t* stanza_create_vcard_request_iq(xmpp_ctx_t* ctx, const char* const jid, const char* const stanza_id);
 xmpp_stanza_t* stanza_create_mam_iq(xmpp_ctx_t* ctx, const char* const jid, const char* const startdate, const char* const enddate, const char* const firstid, const char* const lastid);
 xmpp_stanza_t* stanza_change_password(xmpp_ctx_t* ctx, const char* const user, const char* const password);