Automated testing to exercise website logic

[harrybiddle]

Since not everybody has access to all of the websites in this repo, it can be hard to test whether your PR breaks functionality for, e.g., Amex, if you don't have an Amex account.

It would be nice to also have some tests in the repo that exercise the selenium code.

Some ideas:

• Mock out all Selenium calls
• For example, by bringing back the website mock thing from before
• Or maybe use this: http://pypom.readthedocs.io/en/latest/user_guide.html
• Or by actually serving up a web server, e.g. like this: https://sqa.stackexchange.com/a/13706
• Restructure the Bank files to not hit Selenium directly, then take Selenium out of the equation

[harrybiddle]

I've written an ETE test in #26.

It really isn't testing very much website logic at all, but it's a start!

[harrybiddle]

Further ETE tests are in #30, pending on #29.