Add vCard support

Only nicknames, photos, birthdays, addresses, telephone numbers, emails,
JIDs, titles, roles, notes, and URLs are supported

Due to the synopsis array not having enough space, `/vcard photo
open-self` and `/vcard photo save-self` are not documented properly in
the synopsis section of the `/vcard` command, but they are documented in
the arguments section

Fixed memory leak in vcard autocomplete (thanks to debXwoody)

tests/unittests/ui/stub_ui.c

@@ -1256,6 +1256,11 @@ win_create_plugin(const char* const plugin_name, const char* const tag)
 {
     return NULL;
 }
+ProfWin*
+win_create_vcard(vCard* vcard)
+{
+    return NULL;
+}
 
 char*
 win_get_tab_identifier(ProfWin* window)

tests/unittests/ui/stub_vcardwin.c

@@ -0,0 +1,4 @@
+void
+vcardwin_update(void)
+{
+}

tests/unittests/xmpp/stub_vcard.c

@@ -0,0 +1,79 @@
+#include "ui/ui.h"
+#include "xmpp/vcard.h"
+
+ProfWin*
+vcard_user_create_win()
+{
+    return NULL;
+}
+
+void
+vcard_user_add_element(vcard_element_t* element)
+{
+}
+
+void
+vcard_user_remove_element(unsigned int index)
+{
+}
+
+void
+vcard_print(xmpp_ctx_t* ctx, ProfWin* window, char* jid)
+{
+}
+
+void
+vcard_photo(xmpp_ctx_t* ctx, char* jid, char* filename, int index, gboolean open)
+{
+}
+
+void
+vcard_user_refresh(void)
+{
+}
+
+void
+vcard_user_save(void)
+{
+}
+
+void
+vcard_user_set_fullname(char* fullname)
+{
+}
+
+void
+vcard_user_set_name_family(char* family)
+{
+}
+
+void
+vcard_user_set_name_given(char* given)
+{
+}
+
+void
+vcard_user_set_name_middle(char* middle)
+{
+}
+
+void
+vcard_user_set_name_prefix(char* prefix)
+{
+}
+
+void
+vcard_user_set_name_suffix(char* suffix)
+{
+}
+
+vcard_element_t*
+vcard_user_get_element_index(unsigned int index)
+{
+    return NULL;
+}
+
+void
+vcard_user_free(void)
+{
+}