C++: introduce a project config file field in the projectPart.

This field is used by the generic project manager which passes the
".config" file in it. The advantage is that both the SnapshotUpdater and
the clang code model do not need to do anything smart, but can pass it
directly to the preprocessor.

Task-number: QTCREATORBUG-11390
Change-Id: I44fc7b20afd28fb59608412f2cce86af6f7e7d6b
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>
Core: Delay coreOpened signal emission

This prevents some window restoring flickering.

Change-Id: Iead0e0f2129b969e1de7e22dbf15e641740e40e1
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
gitignore: ignore .qmake.stash files

Change-Id: I6ebea0f6ce680ee95190be68ec2ae96ec04958ad
Reviewed-by: Eike Ziller <eike.ziller@digia.com>