Fix autocompletion inside method t1001218

First attempt at cleaning up ScalaCompletions a little... Most of the code is still the same, but i shifted a few things around / grouped together some functionality.

Changes
1) Added an additional check for the Apply() tree, so that autocompletion works for method application (this is the main fix of the PR)

2) Stopped firing off a JDT search for type member completion, which doesn't make sense.  https://groups.google.com/d/msg/scala-ide-dev/Hh2M4xMN8g4/i0N01KsF6pgJ

P.S. I signed the TypeSafe CLA.