rebar integration: support more than compilation

[vladdu]

When rebar is supported, one should be able to even build releases, etc

[frehberg]

building a release might be realized as "Export" feature

[vladdu]

That's a good suggestion, I didn't consider that option. Thanks!

Another way would be to have special a "release" project that contains the release configuration (it is a separate project because there may be multiple erlang projects in the workspace that need to be packed in the same release). This way we can use an editor for the release config.