[feature] Added the Post class
Added support for Post in FacebookInterface

Also include some unit test cleanups.
Renamed several non-identifiable interfaces

This commit provides renamed interfaces for Facebook
in order to make some interfaces's names more explicit.

Since FacebookPictureInterface got renamed, empty filters
no longer create queries that include pictures. However,
since that the behaviour for empty filters should be changed,
that should not matter a lot.
Merge pull request #21 from SfietKonstantin/feed

[qml-social] Support for post.