multi Scala support

Rework of the build to be able to install multiple version of Scala on one Eclipse installation.
The Scala bundles are grouped in features, which can be installed as needed.

It is working fine, except that some of the dependencies defined in scalariform are not precise enough and create a conflict.
The last commit disable some of the support to be able to work until the upstream problems are fixed. It creates a jar container bundle, with the Scala 2.10 jars, to be able to make the 2.10 jars available in a 2.11 installation.