client: fix cutting/pasting text filter box behavior

Previously if you cut or paste text in the filter box using the mouse,
the search results would not update. Now, they do.

Closes #332
workaround for findit bug. closes #330
client: fix player prediction when currently playing track is removed

closes #327
fix handling of slashes when importing from youtube

closes #322
disable hardware playback button when not admin

closes #285
workaround for last.fm bug. closes #318
fix crash when uploading non-media file

closes #341