Basic Travis-CI setup

[k9ert]

• Ignoring the ResourceWarnings for now
• created a simple Travis-CI setup based on how the HWI did it
• Created a simple functionality to be able to pin the bitcoin-repo in the case that the tests are failing because of changes in the bitcoin-repo. In this case the fix is probably simpler then the functionality.

In order to remove the pinning, simply remove the file test/bitcoin_pin. In order to activate builds on your repo, signup https://travis-ci.com If you get "Abuse-issues", then you have to create a support-ticket. Quickly they assume bad things if people are fiddling with bitcoin-stuff.

[justinmoon]

Hey sorry just saw this now. Looks really nice. I'll try to review soon.