Makes several fixes to clean display of data on template; adds admin function...

* changes template filters to be |default:n/a|default_if_none:n/a sted
* adds if else to containment figure on detail.html
* finishes off default template tag work/experiments
* adds |default:n/a|default_if_none:n/a to relevant areas on index.html… …
* adds location info without map as fallback if no lat/long for feature… …
* sets limit of 3 promoted fires, ordered by date
* removes annoying float issue on 2013 injury display using |floatformat:0
* adds admin action to promote a fire to feature section, or remove it … …
* tries to write a function for saving a fire if it's featured to requi…