Add continous integration using travis

[RKrahl]

Would be nice to have travis automatically run the test suite.

Note that most tests require an ICAT server to connect to. This is really involved to set up with travis.

[fisherab]

I never considered it to be worth the effort for the other components

[RKrahl]

It's a large one time effort that would save a smaller but regular one. So in the long run, it may pay off. Note that for a full test, I use several different Python versions and ICAT/IDS server versions to test with, so the regular effort is still significant.

But I'm not sure that I will ever do it. This issue is more a note to myself to keep the idea in mind.