Reworked the themechooser window in settings-ui.xml.

Tweaked the placement for the searchlist popup window in the streamview,
playlisteditorview_tree and playlisteditorview_gallery windows in stream-ui.xml and music-ui.xml.

Tweaked the placement for the searchlist popup window in the base_play_list_panel group
definition in music-base.xml.

modified:   music-base.xml
modified:   music-ui.xml
modified:   settings-ui.xml
modified:   stream-ui.xml