Move title_format from window to container.

This patch moves the title_format information from windows to containers.
Furthermore, it allows correctly setting it on window-less containers and
displays the title accordingly for split containers.

We now also dump and read title_format in GET_TREE / during restarts.

fixes #2120

src/util.c

@@ -343,6 +343,7 @@ char *pango_escape_markup(char *input) {
 
     char *escaped = g_markup_escape_text(input, -1);
     FREE(input);
+
     return escaped;
 }