IntelliJ IDEA files for version 14

The latest version of the Scala plugin for IntelliJ IDEA introduces
a new project structure

http://blog.jetbrains.com/scala/2014/10/30/scala-plugin-update-for-intellij-idea-14-rc-is-out/

Due to a bug (https://youtrack.jetbrains.com/issue/SCL-7753), you
currently need to install the latest nightly build from here:
http://confluence.jetbrains.com/display/SCA/Scala+Plugin+Nightly+Builds+for+Cassiopeia

The new format doesn't allow scala compiler options per-module, so
the `-sourcepath src/libarary` is used for all modules.
Merge pull request #4087 from lrytz/intellij

IntelliJ IDEA files for version 14