Specify external dependencies

[shntnu]

A test failed because an old version of SQLite was being used by Travis. I handled this 4e45e8f by updating .travis.yml. But this should be likely handled somewhere else, probably in setup.py?
Ditto for other things we specify in addons/apt/packages.

[mcquin]

#37 may help resolve this. pip is only for managing Python dependencies. Anaconda/conda can manage the entire environment, including non-Python dependencies such as SQLite.

(Travis will need to use the conda environment to prevent that failure from recurring.)