* Now when we compile plugins it checks whether plugin's folder
  contains *.jucer file and appropriate Makefile for plugin in the
  Source/ folder.

* All modules are replaced with the JUCE 4.2.1 ones;
* Introjucer was replaced by Projucer;
* Also some appropriate needed fixes for Makefile.plugins;
* Removed -fvisibility=hidden flag for Linux building.