Detect outdated model

Buildship should listen for changes in build files and show a non-intrusive notification that the project model should be synched. The notification should include the button to do that synchronization, so the user only needs one click to do it.

This will come. It will be implemented in Gradle core since there are other scenarios where this information is useful/needed (and Gradle core also knows much better all the places to watch for changes). Buildhip is planned to receive events for file changes detected by Gradle core.