enable Espresso tests with some basic UI tasks

Espresso tests are scripted interactions with the UI. They can provide at the very least so essential smoke tests, like whether the UI loads without crashing. They require an emulator, so they are only useful here if we can get the emulator tests running smoothly. I have written some basic ones that I'm posting here for others to try. Once the emulator runs are stable, I'll work on getting it merged.

While I was at it, I merged the relevant changes from !543 (closed) manually, and fixed up the lint stuff for the build flavors.