Add tests for sendEmail.

Add isSendable flag.
Reset sinon stubs on global stuff.

Clean up super adhoc test.
Remove ETahi.reset() where it's not needed.

App.reset() removes objects from the application container and
resets teh route.  Isolated tests don't really need to interact
with either of those.  Integration tests and tests that use
ETahi.__container__ will still need to do a ETahi.reset() on teardown.
Remove redundant capybara spec.

This functionality is covered by an ember integration test, two unit
tests, and a ruby controller test.