Add support for Travis. Includes a test Gmail account with obfuscated credentials.

To ensure code integrity, we should setup Travis CI.

Probably the reason this hasn't been done is that we need a way for Travis to connect to Gmail.

There are two ways to do this:

1. Use Travis's [encrypted environment variables functionality](http://docs.travis-ci.com/user/encryption-keys/)  This has the drawback that PRs won't be able to use Travis.

2. Store test account credentials in the Gmail gem repo.

Personally, I don't see a huge issue with #2, but to be cautious, I've added a trivial obfuscation mechanism to avoid storing clear text.