Rebuild IncrementalBuilder

This is related to #479. It removes the IncrementalBuilder and related code. This is the first step prior to starting on Scala 2.11 support. The IncrementalBuilder is not supported in Scala 2.11 and in the future we want to handle all build related activities using SBT.

There is associated PR in ensime-emacs to remove the build items from the Ensime menu.