[connections] Update dependencies in README.rst and add setting for m…

[okraits]

…od_spatialite

I'm not sure if I should add the setting for mod_spatialite also to openwisp_controller/connection/settings.py.

[cappe87]

I had the same issues on debian, I installed this libsqlite3-mod-spatialite and added SPATIALITE_LIBRARY_PATH = 'mod_spatialite' in settings.py like the PR and now it works.

[nemesifier]

Let's see if the modified settings.py works on travis-ci

[nemesifier]

Unfortunately, modifying the setting breaks the travis build.

[okraits]

Sorry to reanimate this old PR. Currently settings.py doesn't contain SPATIALITE_LIBRARY_PATH = 'mod_spatialite' which means that every user of openwisp-controller has to manually add that line to his local_settings.py. Shouldn't we better add that line to settings.py and fix the travis build instead?