Varapp-backend-py

New "Variant type" filter (SNP/Indel).

IGV view available.
See docs at:
https://varapp-demo.vital-it.ch/docs/src/usage.htmlviewing-read-alignments
https://varapp-demo.vital-it.ch/docs/src/deploy/bamserver.htmlbamserver

- Fixed concurrency issues when dbs were modified.
- Simplified installation: no more need to pre-download Python libs. Just clone, edit settings and install.
- Available through PyPi (experimental). After `pip3 install varapp-backend-py`, the settings file can be found at "<virtualenv>/lib/python<version>/site-packages/varmed/settings/settings.py" .

- Better dbs management
- No more Cython modules building step is required for installing
- Improved logging