This extends the `float-filter-add` command to allow matching on window
titles as well, using a `float-filter-add kind pattern` syntax. The
following kinds are supported:
* `title`, which matches window titles
* `app-id`, which matches app ids
Only exact matches are considered.
As an example following configuration floats all windows with the title
'asdf with spaces'.
riverctl float-filter-add title 'asdf with spaces'