ENHANCEMENT: Select all/deselect all function checkbox

[carlvlewis]

When trying to view only one or two of the taxonomies, it gets tedious having to uncheck the rest first. We should add a select/deselect all function.

[royemosby]

note to self...

<label><div><input type="checkbox" class="leaflet-control-layers-selector" checked=""><span>Toggle all</span></div></label>

prepend toggle to .leaflet-control-layers-overlays

[carlvlewis]

Sawweeeett. I think I can make that patch if you don't get to it first.

[royemosby]

The code above is just the checkbox; it will still need logic behind it. I would like to figure this one out...