Added controller to show report on index page or redirect to new_metric.
Added functional tests for this behaviour.
Added timecop gem.
Added extension method round_to_month for Date and TimeWithZone. Added tests for this method.
Metric month field automatically round to month-year before validation.Added manual rounding for metric factory for tests.
Also added methods to check this month payment status and tests for them.
Fixed bug that was made in previous commit: instead of removing only datetime rounding in controller, i removed whole metric.month assignment line.
Double quotes changed to single quotes for controller action names.
yet another bugfix: there are no 'today' method for DateTime. Changed to 'now'.
New feature: when date is near payment date and there are no data for this month in db - user redirected to new_metric form. Otherwise report for current or last month rendered.