Made it possible to patch IDEA by adding class to idea_runner module.

See confluence page for details: http://confluence.jetbrains.com/display/JET/How+to+patch+IDEA+for+Kotlin
Clarified assertion for EA-53060.
Clarified assertion for EA-45529.
Fixed EA-45529.
Minor. Removed redundant cast.
Clarified assert for EA-45243.
Added test for EA-49318.
Saving only class files into incremental cache.

Fixed exception for JS modules.
Implement modificationTracker for CompositeDiagnostics

 #KT-5981 Fixed
JS backend: test for KT-2901: nullable type in string template
JS backend: fix KT-2468: ArrayList<String> is List<String> or HashSet<String> is Set<String> fails in generated JS code
JS backend: tests for KT-2468