CppEditor: Add refactoring operation to move definition of a function

With this new operation it is possible to move a function definition
from a cpp file to the header file or vice versa. One can also move a
function definition outside the class body.

Task-number: QTCREATORBUG-516
Task-number: QTCREATORBUG-5364
Change-Id: Id3daefe79284bd9086282369c9d251e003951c11
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>