C++: Changes in semantic highlighting

- Fix issues with virtual/non-virtual destructors. They were not
  being correctly identified in some cases - in particular on certain
  uses in derived classes.

- Since now we do have a highlighting item for regular functions,
  constructors and destructors are now highlighted as such. This is
  more semantically correct and actually makes navigation and readiblity
  more distinguishable, since it cleary differentiates the type itself
  from its uses in expressions and declarators. (This seems to be what
  other IDEs like Eclipse, Visual Studio, KDevelop are doing.)

  NOTE: There's a switch to disable this item in the case it doesn't
  get good acceptance. Actually, the switch can be made a user
  setting...?

- Change the default color scheme so regular and virtual functions
  have the same color (virtuals continue to be italic). This makes
  sense given the above mentioned changes in constructors/destructors
  highlighting behavior. (In other schemes virtual funcions don't have
  different color, so this shouldn't be necessary in those.)

- Small renaming: "members" are now "fields" - consistent, since
  they apply for data and it's the term used in the UI.

Change-Id: Ib1aa9c0bbf28a31d09f5696460b0095fbe29de80
Reviewed-by: Roberto Raggi <roberto.raggi@nokia.com>