Move OMERO documentation to omero/ subfolder
Fix compilation by pointing at the themes/ directory
Remove formats from excluded patterns in OMERO documentation
Move shared configuration settings to common configuration file

- Common configuration moved to common/conf.py
- Move themes to common/
Add central Makefile to build OMERO & Formats documentations at once

Also allows Travis script command to remain unchanged
Merge pull request #315 from sbesson/doc_reorganization

Doc reorganization