* 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.

* Added custom audio processor editor for CAR plugin - CAREditor;
* Added buttons to switch between "Reference" and "Affected" channels;
* CAR processor some minor changes;
* Some minor changes in GenericEditor class which provide more
  possibilities for plugins (e.g. plugins can implement their own
  resized() methods, etc.);
* Added UIUtilities header file in which we can include any
  UI components/utilities which will be useful for easier plugin
  creation.

* 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.

* Since "Small text" renders very bad, without any hinting, we replace
  it by "Default" font.  And also "Default" font is much more suitable
  for Material Design.
* Adjusted font sizes.

Mac build fixes

Merge branch 'filereader_adjustments' of https://github.com/sept-en/plugin-GUI into sept-en-filereader_adjustments

* Adjusted positions for play, record, master clock components;
* Adjusted positions for CPU and Disk meter components;
* Stylystic fixes.

* Implemented sliders' material lookAndFeel;
* Material lookAndFeel have been applied to sliders;
* Improved UI layout for panel.
* Adjusted positioning of elements during resizing.
* New icon for "Mute" button;

FileReader: added possibility to drag&drop files. Refactoring and stylystic fixes. 

When double clicking on a channel to set fullscreen, the channel height
was set to 0 because the textbook wasn’t set to a correct selected
index. This now gets the value from the text, so it should work
regardless of how the value was entered.