Support for gradle 1.6 and above, and more (fixes #9, #10)

* Removed explicit project/module plugins
* Scala Facet can optionally be generated for root project.
* Refactored settings objects into separate project/module settings
Repackage to com.github.rodionmoiseev.gradle.plugins (fixes #11)

* Renamed artifact name: 'idea-scala-plugin' -> 'idea-scala'
* Build script fixes