Allow filtering by category type

[jasonlally]

Add a filter for the high level categories (multiple select). This can be optional. There are fewer of these, it'll make it easier to limit the returns. Could also just be implemented as a checkbox on the legend after the initial data is returned.

[jasonlally]

API docs here: https://dev.socrata.com/foundry/data.sfgov.org/cuks-n6tp

You can see the categories + counts with this query for example: http://data.sfgov.org/resource/cuks-n6tp.json?$select=count(*),category&$group=category

[paulhennings]

Cross reference to issue #48

[sarah-clements]

I'll take a stab at this.

[paulhennings]

This is dependent on Issue #48 being completed first, so that the "Clery Category" is available for reporting.
Update 3/15/17: Issue #48 is complete. This can proceed.

[paulhennings]

Research on this didn't find a fully functional filter option. Options in "vanilla javascript" don't allow multi-select. Multi-select would require React or another advanced framework. For now, let's follow our "keep is sweet and simple" rule. Moving this to the Parking Lot and we can research again in a few months to see if there are new library options that might work.