Get cross.png from the resource bundle instead of the resource path.
Make StatsManager announce stat updates via a signal.
Add StatModel, a QAbstractTableModel for representing a list of stat objects.
Add ControlModel, a QAbstractTableModel for representing a list of controls.
Add DlgDeveloperTools, a dialog with various useful debugging tools.

* A controls tab where you can see and edit Mixxx's controls directly.
* A stats tab where you can see the stats (e.g. average soundcard callback
  durations) that Mixxx tracks in realtime.
* A log tab where you can see the Mixxx log without having to go find it on the
  filesystem.

The tables are set to update at 2FPS which seemed like the right balance between
CPU overhead and interactivity to me.
Add a Developer Tools option to the Developer menu. Now we're cool like Chrome :).