Add experimental clang code-model plug-in.

Previously known as the wip/clang branch.

Contributors (in alphabetical order):
- Christian Kamm <christian.d.kamm@nokia.com>
- Erik Verbruggen <erik.verbruggen@digia.com>
- Leandro Melo <leandro.melo@nokia.com>
- Peter Kuemmel <syntheticpp@gmx.net>
- Sergey Shambir <sergey.shambir.auto@gmail.com>

Change-Id: I4c3ff600a19b6732641c1d5ef28236bf2cc17737
Reviewed-by: hjk <hjk121@nokiamail.com>