move Group/Report under presenters/
move all relative time logic into metric presenter
Merge pull request #40 from afeld/presenter

@fancyremarker => refactor relative time logic into presenters
Merge remote-tracking branch 'upstream/master' into list

Conflicts:
	lib/tricle/group.rb
	lib/tricle/metric.rb
	lib/tricle/report.rb
	lib/tricle/templates/email.html.erb
	spec/app/group_test_mailer.rb
	spec/presenters/metric_spec.rb
	spec/unit/report_spec.rb