Add setting to not colorize own nick according to xep-0392

Some users might want there nick to always stay white (etc) for easier
recognition.

Now we can do `/color own off` to not generate the color based on
xep-0392. The `me=` color (etc) from the theme will then be used.

Once we run this command `theme_load()` is called again.
And the theme looks totally wrong.
We encountered this at other times already and I think it's nothing
wrong with this new code here now but that there seems to be a missing
closing attr for the color when drawing.

Should be investigated seperately.

Fix https://github.com/profanity-im/profanity/issues/1288

src/config/preferences.c

@@ -1745,6 +1745,7 @@ _get_group(preference_t pref)
         case PREF_CONSOLE_PRIVATE:
         case PREF_CONSOLE_CHAT:
         case PREF_COLOR_NICK:
+        case PREF_COLOR_NICK_OWN:
         case PREF_ROSTER_COLOR_NICK:
         case PREF_OCCUPANTS_COLOR_NICK:
         case PREF_STATUSBAR_SHOW_NAME:
@@ -2033,6 +2034,8 @@ _get_key(preference_t pref)
             return "console.chat";
         case PREF_COLOR_NICK:
             return "color.nick";
+        case PREF_COLOR_NICK_OWN:
+            return "color.nick.own";
         case PREF_ROSTER_COLOR_NICK:
             return "color.roster.nick";
         case PREF_OCCUPANTS_COLOR_NICK:
@@ -2123,6 +2126,7 @@ _get_default_boolean(preference_t pref)
         case PREF_STATES:
         case PREF_OUTTYPE:
         case PREF_TITLEBAR_MUC_TITLE_NAME:
+        case PREF_COLOR_NICK_OWN:
             return TRUE;
         default:
             return FALSE;

src/config/preferences.h

@@ -151,6 +151,7 @@ typedef enum {
     PREF_CONSOLE_PRIVATE,
     PREF_CONSOLE_CHAT,
     PREF_COLOR_NICK,
+    PREF_COLOR_NICK_OWN,
     PREF_ROSTER_COLOR_NICK,
     PREF_OCCUPANTS_COLOR_NICK,
     PREF_BOOKMARK_INVITE,