Fix for KT-5420

Fix for [KT-5420](http://youtrack.jetbrains.com/issue/KT-5420)
Kotlin compiler has a dependency on Idea open api, which has static initializations that prevent garbage collection of classloader that loaded kotlin plugin's core.
This causes severe memory leak when used in combination with Gradle's deamon process, as new classloader was created on each project model evaluation.
Now classloader will only be created once per kotlin version in use. This should work fine as long as Gradle deamon reuses plugin classes and does not reload them.

Otherwise, [ZipFileCache](https://github.com/JetBrains/intellij-community/blob/ff16ce78a1e0ddb6e67fd1dbc6e6a597e20d483a/platform/util/src/com/intellij/openapi/util/io/ZipFileCache.java) and [LowMemoryWatcher](https://github.com/JetBrains/intellij-community/blob/8f2f40ec87a24097b2f3eb37ceca85397ea507a0/platform/util/src/com/intellij/openapi/util/LowMemoryWatcher.java) will need to be excluded from bundled idea open api, or fixed.