WM: Moved leaflet map controls to bottom left, closes #716
1. Placing the leaflet controls using the JS api rather than overriding .leaflet-top etc. 2. Adding the down arrow icon to the View By menu in CLJS and 3. Resizing the layers control to 30px (the image is 28px, 1px padding).
Merge pull request #735 from onaio/716_move_map_layer_control

WM: Moved leaflet map controls to bottom left, closes #716