Use environment variables with two email addresses

This is another attempt at fixing #1.

To support reviewers with a different Git-configured e-mail address and code
review addresses, the environment variable REVIEWERS must be adjusted to store
both of these addresses per reviewer.

NB: As this commit makes use of the new structure, it breaks the previous setup.
Merge branch 'sindrenm-bug-fix/01'

Conflicts:
	lib/application.rb