Introduce codemodelbackend process and library

This is a partial result of wip/clang-oop. More will follow.

This allows us to invoke the completion out of the Qt Creator process
and thus safes us as against libclang crashes.

At this point only the completion use case is supported.

Some notes on the individual components:

 src/libs/codemodelbackendipc
  * library encapsulating the inter process communication handling
  * used by the backend application and in a follow-up change by the
    creator integration

 src/libs/3rdparty/sqlite
  * version 3.8.10.2
  * dependency of codemodelbackendipc, will be used to storage indexing
    data, among others

 src/tools/codemodelbackend
  * the backend application

 tests/unit:
  * unit tests

Change-Id: I91a48e27467581a22fb760a18d8eb926008fea60
Reviewed-by: Alessandro Portale <alessandro.portale@theqtcompany.com>
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@theqtcompany.com>
Reviewed-by: Marco Bubke <marco.bubke@theqtcompany.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>