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
This should be the last commit that formats a big bunch of files. From
here on, whenever I merge patches, I’ll run clang-format like described
in the title.
This avoids flooding stdout every time some text (e.g. a window
decoration) is drawn, yet leaves the message in place when it’s actually
relevant (upon DPI changes).
fixes#1115
