Changeset: ThisContext styling

Hi all! :-) Please have a look at the following changeset.

It provides correct styling (and auto-completion) of the ThisContext identifier in context-dependent styling environments.

Before:

After:

Some notes:

• #doItInContextName still feels a bit too hard-coded, but I'm really not sure into which class this constant could belong instead.
• (OT, general to the concept of #DoItIn:: It feels a bit suboptimal that in the following example, you cannot access the temporary from the ContextVariableInspector code pane as it's shadowed:
  
  But especially in this no-pattern scenario, choosing a different identifier to provide thisContext would be confusing either, hm ...
  And if we merge this changeset, there will be also a cheap workaround, so maybe we already have the best solution?)
• The changeset also extends Autocompletion, but of course, the changes in Trunk don't depend on Autocompletion. If you agree to merge the changeset, I will try to integrate the completion-specific changes into Autocompletion.

As always, any feedback is highly welcome! :-)

Best,

Christoph