IDEA-109519 Gradle: Don't ignore user-defined settings on initial project import
project mem leak
IDEA-111626 External System tool window: selected task could be executed on pressing Enter
Merge remote-tracking branch 'origin/master'
IDEA-111910 External system: Make it possible to customize processing classpath in case of in-process mode

1. Exact GradleProjectExtension implementation class is used at in-process mode now (implicitly exposes classpath of the plugin where the extension is defined);
2. Added ability to apply custom explicit classpath defined by the GradleProjectStructureExtension;