Add functionality to Intellij Idea plugin

It'll be helpful if Intellij Idea plugin can help with some repeatable actions.
A few ideas to start.

1. rename field -> rename properties in the java resource bundle
2. usage of properties in resource bundle (find usages, via references, it's the same mechanism as in the first 1)
3. add a new property to the resource bundle (quick fix action)

I think we also may want to move the build of the plugin from the maven one into Gradle. Jetbrains has a special one for that https://github.com/JetBrains/gradle-intellij-plugin