Issue #1211: Load fonts in background after startup.

Fonts should not be blocking startup as this provides a very bad
experience when people have a lot of fonts. This was experienced even
more on Windows where loading time are often excessively long.
We were already running font loading in a thread, yet were still
blocking startup (thread was only so that the loading status GUI could
get updated as a feedback). Now we will only start loading and proceed
directly to next steps.
While fonts are not loaded, the text tool will not be usable, yet all
other activities can be performed.

(cherry picked from commit 2484dec7d5)

app/core/gimp.c

@@ -799,8 +799,8 @@ gimp_restore (Gimp                *gimp,
   /*  initialize the list of fonts  */
   if (! gimp->no_fonts)
     {
-      status_callback (NULL, _("Fonts (this may take a while)"), 0.7);
-      gimp_fonts_load (gimp, status_callback, error);
+      status_callback (NULL, _("Fonts"), 0.7);
+      gimp_fonts_load (gimp, error);
     }
 
   /*  initialize the template list  */