update gradle-api artifact to version 1.6 this is required to make kotlin gradle plugin compatible with upcoming Gradle 2.0
cleanup Gradle API deprecation warnings to make plugin compatible with upcoming Gradle 2.0. This includes moving minimum compatible version from 1.4 to 1.6
Update to IDEA 135.815 EAP
Smart completion after == and !=

 #KT-4912 Fixed
Smart completion: more correct Tab key handling

 #KT-4954 Fixed
Smart completion: checking constructor's visibility + true and false for Boolean

 #KT-4916 Fixed
Smart completion: "null" when nullable value expected
Smart completion: auto-cast to non-null type is not recognized for field from constructor

 #KT-4906 Fixed
Smart completion for then and else branches of if

 #KT-4910 Fixed
No more java lookup elements in code completion (except for one case)
Smart completion: only overloads with all previous arguments matched are considered
Minor rename
Fixed mock jdk
Smart completion: added test for KT-4929 fixed by svtk
Smart completion should not suggest variants for private signatures

 #KT-4899 Fixed
Smart completion after ?: works incorrectly

 #KT-4926 Fixed
Smart completion works for block's result
Added test data for future use
Added utility extension methods to not use TypeUtils
Smart completion: fixed logic in elvis operator