* Updated images for collapse/show button;
* Updated animations;
* Some other small UI improvements;
* Added possibility to collapse element by clicking "ESC" key
  either on the component itself or on the TextEditor.

* Created SlicerChannelSelectorComponent class which holds inside
  all ChannelSelector's parser related components and which
  takes responsibility for parsing selected range, etc.
* Added possibility to collapse parser related components.
* Added animations.
* UI improvements.
* Minor bugs fixes.

Set MACOSX_DEPLOYMENT_TARGET (i.e. the minimum supported OS X version) to 10.9.  Pass -Wpartial-availability to the compiler so it will warn about usage of API's that aren't available on all supported OS X versions.  Removed /opt/local and /usr/local from OS X header and library search paths, as they're used only by specific plugins and not needed generally.

* 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 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.

* Implemented ButtonGroupManager.
  It is responsible for positioning of buttons, any animations
  during switching, etc.
* Added MaterialButtonLookAndFeel class which implements
  flat button look and feel following Google Material Design Guidelines.

On OS X, copy Rhythm-related files to the application bundle's Resources folder, and use the bundled copies at run time