Add title_align config directive

Controls the window titles alignment in title bars. Possible values are:
- left
- center
- right

Co-authored-by: Orestis Floros <orestisf1993@gmail.com>
- Made title_align a config directive instead of a command. Helps with
some tree_render() issues we had.
- Made title_max_width the same for all 3 cases.
- Modified title offset calculations and added explanations for each
case.
- Append title_padding to mark_width if a mark exists.

Fixes #1750

include/configuration.h

@@ -201,6 +201,13 @@ struct Config {
      * decoration. Marks starting with a "_" will be ignored either way. */
     bool show_marks;
 
+    /** Title alignment options. */
+    enum {
+        ALIGN_LEFT,
+        ALIGN_CENTER,
+        ALIGN_RIGHT
+    } title_align;
+
     /** The default border style for new windows. */
     border_style_t default_border;