Default hits to last 30 days instead of all time

* Switch from All time to last 30 days
* Show more relevant errors and load pages faster
* Tweak feature so there’s a difference between 30 days and all time
* Use Timecop to freeze time in feature and specs
Merge pull request #207 from alphagov/update-default-analytics-time

Default hits to last 30 days instead of all time