Reworked the window manager in video-ui.xml.
Added the base definition of base_arrows_backdrop.
Various tweaks to previous reworked windows.

modified:   base.xml
modified:   browser-ui.xml
modified:   images/masks/manager_coverart_mask.png
modified:   news-ui.xml
modified:   recordings-ui.xml
modified:   schedule-ui.xml
modified:   status-ui.xml
modified:   video-ui.xml