Prevent unnecessary art file operations

When writing album art, the scanner was rewriting art files for an
album as many times as there are songs in the album.

This patch makes the scanner only write art files once per album.
Merge pull request #58 from williamjacksn/art-scan

Prevent unnecessary art file operations
Save audio volume
Fix every rating being orange in timeline
Have wifi icon always show
Better ldetect logging
Fix album_diff not being sent
Change Kevin to SOcean in about page
Fix ldetect remove
and again (really wish I could test locally)
Expand listener detection
More ldetect agents, fix audio volume pref
More audio pref fixes
And again with more ldetect agents
fix anon user extended history (plus agents)
Workaround for lack of performance.now
Fix anonymous voting
Merge branch 'master' of https://github.com/rmcauley/rainwave
Hotfix for syntax error
Fix audio volume not redrawing properly