Summary:
- Sets up spectron test suite inside its own directory and with its own
dependencies (must run on a build of the app)
- Sets up dummy test
- Adds `run-spectron-specs` grunt task, and adds it to cibuild task
- Cleans up spec tasks code
Test Plan: - Run specs
Reviewers: evan, bengotow
Reviewed By: bengotow
Differential Revision: https://phab.nylas.com/D2256
