Add missing PiP icons from web devel kit. Also add play/pause
icons at the right size and remove all workarounds/scaling
implemented or these two.
Playback icons are always two bars for pause and triangle for play,
so hopefully this will not be problematic, as this guaranties the
right size for them that Adwaita unfortunately cannot provide.
Use the new "pip-in" and "pip-out" GNOME symbolic icons if user theme has them for enter/leave floating mode button. When icon is unavailable on the host, old icon will be used instead.
This avoids D&D controllers clash and allows to freely customize how maximize, minimize and close buttons work (differently for e.g. web application) and where are they placed
The "clapper_src" directory name was unusual. This was done to make it work as a widget for other apps. Now that this functionality got removed it can be named simply "src" as recommended by guidelines.
