Add e2e tests

[jwasilgeo]

We should have e2e sepcs for each test page. After PR #137, we will need to add:

• custom-directive
• legend
• other-esri-modules

[tomwayson]

I'm not sure about custom-directive - basically the only part of this library that that page uses is esri.core, and I'm assuming that's thoroughly covered by the other tests.

Same w/ other-esri-modules. I don't know if that uses any part of the module that is not covered by other tests.

I didn't realize that we didn't have a test for legend. We should definitely add that.

[jwasilgeo]

Good points above