Add switch for enabling/disabling EMS heatmaps

[meilinger]

Need to be able to turn off heatmaps in the next release to production as we'll be merging develop into master. Add a setting in settings.py in order to either enable or disable EMS heatmaps. If EMS heatmaps are disabled then the end-user shouldn't have the option to view them on department detail pages.

[josellausas]

Starting on this