Fetch markets in a better, faster way. Fixes #186.
Changes chart download icon to a download icon. Removes cog thing.
Fixed bug in the backend where a ValuesList could not be JSON
serialized. Added time filter stuff to the report pages.
Removing cruft.
Adds 'Average Cost over Time' timeseries chart.
Fixed more values_list bugs.
Added frequency of resources charts as per #195.
Stuff to get Bought vs. Caught occurrence graph correct.

- Spelled occurrence correctly
- Fixed bug on the backed involving difference in answers per crosstab.