Introduced Flat variant of the Dark Theme
Performance Fixes
Minor layout fixes
Revert "Fix timestamp alignment in Last.fm popover"

This reverts commit 93e259c1f651ee6025f9c66f28103531fb5678db.
Remember last size of mini player (fixes #96)
Revert event tap creation, fixes QuickLook but breaks Fireworks (fixes #117)
Modify dark.css, CustomWebView to use/hold inverted sprite sheet (fixes #90, #120)

Previously, many things were made to match the dark style by using the
`-webkit-filter: invert(100%)` idiom in CSS, but this had a huge
performance impact since it was used for every thumbs up in every row,
on every player button, and so on.

To get rid of the performance hit, I instead download the sprite sheet
at the beginning of the program and invert the colors in memory. The
CSS is then updated to point to a special URL
(http://radiant-player-mac/sprites-inverted.png) at which point Radiant
Player returns the inverted image and the performance hit is now gone
as the inverted sprite sheet is now handled as a regular image.

In any forthcoming dark themes or derivatives of the built in theme, if
you need an inverted version of a particular sprite, set the
background-image to this special URL.
Fix mini player to work on OS X 10.8 (fixes #106)
Fix CSS for Safari 6 and OS X 10.8 (fixes #91)
Fix notifications on Safari 6/OS X 10.8 (fixes #92)
Tweak preferences window height
Use an NSURLProtocol instead of data: URIs (fixes #123)
Fix mini player location at edge of screen, multiple screens (fixes #108)
Merge branch 'master' into pr/105

* master: (24 commits)
  Fix mini player location at edge of screen, multiple screens (fixes #108)
  Use an NSURLProtocol instead of data: URIs (fixes #123)
  Tweak preferences window height
  Fix notifications on Safari 6/OS X 10.8 (fixes #92)
  Fix CSS for Safari 6 and OS X 10.8 (fixes #91)
  Fix mini player to work on OS X 10.8 (fixes #106)
  Modify dark.css, CustomWebView to use/hold inverted sprite sheet (fixes #90, #120)
  Revert event tap creation, fixes QuickLook but breaks Fireworks (fixes #117)
  Remember last size of mini player (fixes #96)
  Revert "Fix timestamp alignment in Last.fm popover"
  Fix timestamp alignment in Last.fm popover
  Update Last.fm API keys
  Add preference to automatically love/unlove a track on Last.fm based on thumbs up rating (fixes #83)
  Add preference for showing the Last.fm button
  Add ability to love/unlove song from Last.fm popover
  Append Last.fm icon instead of replacing other links
  Add Last.fm popover that shows 10 most recent tracks
  Add NSDate+TimeAgo to podfile
  Update Last.fm icon in preferences
  Fix album title color in dark style (fixes #101, thanks @Deanmv)
  ...
Update, tweak dark flat style (thanks @hoffi very much!)
Merge branch 'pr/105'

* pr/105:
  Update, tweak dark flat style (thanks @hoffi very much!)
  Minor layout fixes
  Performance Fixes
  Introduced Flat variant of the Dark Theme
Fix check for 10.9 API in preferences window
Respond with color change of mini player's "show main window" button (fixes #124)
Add advanced preferences, pref. for event tap creation (fixes #40)
WIP spotify black style