Sphinx api improvements (rebased onto develop)

This is the same as gh-2615 but rebased onto develop.

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Following @rleigh-dundee's effort to convert the aut-generated Python API to use Sphinx, this PR makes cosmetic adjustements to the generated API for proper inclusion/announcement with the 5.0.3 release:
- pass the release number to the documentation (same as javadoc and slice2html)
- re-import the configuration from ome-documentation and simplify `conf.py`
- redirect the main overview page to point at `python` rather than `epydocs`
- use OMERO.py rather than OmeroPy
- include the OME logo (svg version - to be tested udner various browsers)

The output of this PR should be published and reviewable under http://ci.openmicroscopy.org/job/OMERO-5.1-merge-build/ICE=3.5,label=ome-c6100-3/javadoc/python/ (or whatever Ice version you choose).

Items not included in this PR but will be part of future work:
- drop `epydocs` completely. As @rleigh-dundee suggested, we can either do that on 5.1.x solely and preserve it on the 5.0.x line or in-between 5.0.3 and 5.0.4
- redirect all the documentation Python api linksto `python`: this requires the Sphinx-generated API to be published. This is very likely a post-5.0.3 release item /cc @hflynn
- fix the docstrings: as discussed previously this is a larger body of work involving rebase issues and should be tackled independently (summer project?)