Fix CAR plugin loading on OS X, compiler warnings

Include definitions of LinearSmoothedValueAtomic's template methods in its header file (required because the explicit instantiations built in to the OE application are not visible to plugins on OS X)

* This class position buttons inside itself
  as tiles and has feature which gives
  us fuzzy button selection possibility via
  mouse drag (or SHIFT+mouse drag for deselection).

* LinearButtonGroupManager class now have the same functionality as
  ButtonGroupManager class had before.
* ButtonGroupManager now is the base class for all other button group
  managers.
* Appropriate fixes in the CAR plugin.

Implemented utilities to get rid of race conditions in plugins (now used in CAR plugin only)

* Implemented LinearSmoothedValueAtomic class based on the
  JUCE 4.0 library' LinearSmoothedValue class but with some improvements
  that were suggested by Timur Doumler during his JUCE Summit 2015
  talk.
* LinearSmoothedValueAtomic is very convenient to use with float values
  that need linearly smoothed behaviour (like volume, etc.) and which
  are shared between several threads (i.e. audio and GUI).
* This class guarantees we won't have any race conditions and it will
  remains lock-free because of using std::atomic inside it.

Add new CAR files to Xcode project

CAR: fixed bug gain slider had per-channel functionality. Other minor fixes.

* ParameterSlider: added possibility to change rotary fill colour.
* CAR gain slider: changed rotary fill colour.

* Fixed bug gain slider have some buggy per-channel functionality
  so it were possibility to set different gain values for only some
  channels.
* Now gain slider affects all the channels.
* Explicitly added gain slider to the CAREditor component.

OS X packaging improvements

CAR plugin major improvements.