WIP Deere skin updates

This PR is about updating the Deere skin to a (at least) usable state for the next pre-release.
Fixes https://bugs.launchpad.net/mixxx/+bug/1380138
Fixes https://blueprints.launchpad.net/mixxx/+spec/1.12-skins

It is WIP, and i`m pleased to add your suggestions.
Just throw your ideas.

For now, nothing spectacular has happened, mostly fixing basic stuff.
1st priority is adding/completing functionality, styling comes later.

**What is planned**
- [ ]  Add dedicated Waveform zoom buttons
       - *Note*: We can have a ``[+]`` and ``[-]`` button, but we can currently not have a ``Reset to default`` button, because of the unusual range of the waveform zoom. Also i would suggest to change the waveform zoom synchronization preferences to be ``On`` by default.
- [ ] Add more Hotcue buttons,  8 or even more?
- [x] Add a dedicated microphone rack for all 4 mics with full control over the input.
     - [ ] FX routing
     - [x] VUmeters
     -  [x] Pregain& mute
     -  [x] Ducking
- [ ] Add ``Preview`` deck
- [ ] Add a deck input selector (combobox?), that allows to switch to AUX on the fly.
- [ ] Add ``Slip mode`` indicator
- [ ] Add different view modes for the decks, that differ in the level of informations.
     - Note: There seems to be a bug with ``<Widgetstack>``, see https://bugs.launchpad.net/mixxx/+bug/1394354
- [ ] Add ``loop move`` and ``loop jump`` controls
- [ ] Add ``Kill``buttons for the 3 EQ bands
- [ ] Add beadgrid edit widget that allows to widen, narrow, set, and match beatgrids. Basically cram all beatgrid controls together into one widget.
     - Note: Can you help with ``QSS`` here, so that a widget becomes visible, once the mouse hovers over another specific widget? 
- [ ] Add ``<Starating>`` widget to the decks, that allows to rate loaded tracks.
      - Note: Can you help with styling the starrating widget? see comment in #381
- [ ] Add recording button
- [ ] Add status indicators for Broadcasting, Vinylcontrol, (Soundmanager)
- [ ] Add functionality to existing sampler decks
- [ ] Add ``TooltipId`` for all controls