In EQ preferences pane, lay out checkboxes vertically like elsewhere. Also add some tooltips.
If a playlist is locked in the History, disable the `Join with Previous` option in the right-click menu
Add alternative American Audio VMS2 controller mapping.

The mapping for VMS2 that comes with Mixxx lacks in some places.
This is an alternative mapping that also supports the rotational
knob for browsing that is not found on the VMS4.
Also secondary loop controls (previously unused) are mapped to
kill switches and some other minor improvements.
Apply some cleanup to VMS2 that is also proposed for VMS4.

Builtin Play and Cue handlers can be used instead of script binding.
We still keep the pause handler for the dedicated pause button.
More cleanup in VMS2 scripts. Remove now unused variables.
Reset to Defaults button in EQ preferences sets EQs to enabled and activates static EQs
Merge pull request #164 from esbrandt/fixit

Small EQ preference pane edits
Merge pull request #163 from snue/feature/aavms2

Alternative mapping for American Audio VMS2