Add ebitda monthly measure

For https://github.com/theodi/dashboards/issues/123
Add events metric
Merge pull request #137 from theodi/events-hosted

Add events metric
Merge pull request #136 from theodi/ebitda-monthly

Add ebitda monthly measure
Merge branch 'refs/heads/master' into income-to-bookings

Conflicts:
	lib/company_dashboard.rb