Merge pull request #198 from skyluc/issue/API-ScalaCompletionProposal

Adapts to ScalaCompletionProposal update
Regularize usage of Utils.WithAsInstanceOfOpt
Regularize usage of EclipseUtils
removing useless usage of SWTUtils
constraining usage of OSGIUtils
Merge pull request #199 from huitseeker/pre/UtilsAPI

cleanups as a prelude to Utils API
Adapts to generic syntax colouring preference page
Adapts to ScalaSyntaxClass cleanup
Adapts to the new syntax parsing API