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

testcases/t/201-config-parser.t

@@ -497,6 +497,7 @@ my $expected_all_tokens = "ERROR: CONFIG: Expected one of these tokens: <end>, '
         fake-outputs
         force_display_urgency_hint
         focus_on_window_activation
+        title_align
         show_marks
         workspace
         ipc_socket