Fixing Scala integration with IntelliJ with new plugin

Intellij Scala plugin (from 0.3.2x) has changed which means that for integration to work fine, we need to add the following to the maven scala plugin section in server/core:

<configuration>
<scalaVersion>2.8.0</scalaVersion>
</configuration>

Afterwards, when configuring the maven facet select the 2.8 compiler bundle.

http://devnet.jetbrains.net/message/5269638

I'll update the scala wiki accordingly.