Introduced mime-type for ObjC++.

Updated/fixed the code to treat treat text/x-objcsrc and
text/x-objc++src correctly.

Change-Id: I1ab97577c786a28381398e4e0fac177325d00d7b
Reviewed-by: Sergey Shambir <sergey.shambir.auto@gmail.com>
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>