Experimental branch for Android support

As part of our project (under supervision of @synctext), we are trying to get (most of) the Tribler core running on Android using the Python for Android runtime. To do this, we have to make several changes to the Tribler code.

This branch should not be merged and is only to take advantage of the @tribler-ci bot to test our changes and make sure we don't break Tribler on other platforms in the progress. Once we got the parts we want to use running, I'll submit another properly cherrypicked pull request.