Rework sphinx documentation

- move all docs sources to docs/source;
- rework documentation structure and contents;
- update conf.py and clean it up;
- switch use oslosphinx;
- add sphinx and oslosphinx to test requrements.

Change-Id: Ied37f86e559516ef7a106e2870d4817ff01a8af4
Merge "Rework sphinx documentation"