Moved SBuild Resolvers into separate Plugins (Support for SBuild 0.8)

With this PR, The SBuild Eclipse Plugin is able to use multiple resolvers. These resolvers will be found in the OSGi service registry and the common resolver interface is pure Java, so that the resolvers can be implemented in different and even binary incompatible Scala versions. The way resolvers are found is using the OSGi whiteboard pattern. As there is no way to ensure, the resolver bundles are active, the plugin scans once after the start of Eclipse all non-active bundles for a special OSGi manifest entry "SBuild-Service" and if one is present, it activates these bundles.

I added two resolvers based on the one previously used in the SBuild Eclipse Plugin, which used the SBuild embedded API. The SBuild07Resolver uses Scala 2.10 and the SBuild08Resolver uses Scala 2.11. This resolved issue #11.

Also, this PR adds an (for now) empty "SBuild" preferences page. Both resolver also add sub preferences pages where the SBuild installation path can be configured. This is related to issue #6.

As, with this change, the SBuild Eclipse Plugin is independent of the Scala version used for SBuild resolver, I also used the opportunity to raise the Scala version to 2.11 for the plugin project.