Change theme handling

So far when loading a theme it also overwrote the preferences the user
set.

Lengthy discussion can be found at
https://github.com/profanity-im/profanity/issues/1077

Now we use `/theme load themename` to load the [colours] part of a
themem only.

`/theme full-load themename` will load the complete theme including
preferences set in there.

Regards https://github.com/profanity-im/profanity/issues/1077

src/config/theme.c

@@ -154,7 +154,7 @@ theme_init(const char *const theme_name)
     g_hash_table_insert(defaults, strdup("untrusted"),               strdup("red"));
     g_hash_table_insert(defaults, strdup("cmd.wins.unread"),         strdup("default"));
 
-    _load_preferences();
+    //_load_preferences();
 }
 
 gboolean
@@ -174,12 +174,14 @@ theme_exists(const char *const theme_name)
 }
 
 gboolean
-theme_load(const char *const theme_name)
+theme_load(const char *const theme_name, gboolean load_theme_prefs)
 {
     color_pair_cache_reset();
 
     if (_theme_load_file(theme_name)) {
-        _load_preferences();
+        if (load_theme_prefs) {
+            _load_preferences();
+        }
         return TRUE;
     } else {
         return FALSE;

src/config/theme.h

@@ -143,7 +143,7 @@ typedef enum {
 
 void theme_init(const char *const theme_name);
 void theme_init_colours(void);
-gboolean theme_load(const char *const theme_name);
+gboolean theme_load(const char *const theme_name, gboolean load_theme_prefs);
 gboolean theme_exists(const char *const theme_name);
 GSList* theme_list(void);
 void theme_close(void);