openlayers: Moved images into "img" folder

This is the original name of the folder in the openlayers project
openlayers: Removed unused styles from CSS file
openlayers: Added ol-ZoomControl.css file
openlayers: Improved zoom control styling
openlayers: Use id instead of class for layer switcher elements

This resolves a conflict with the global .box class and the layer switcher
openlayers: Improved layer switcher control styling
config/default: Set ASSETS_DEBUG to False
openlayers: Added checkmarks to layer switcher styling
openlayers: Moved checkmark to the lower right corner
Merge pull request #85 from Turbo87/map-css

Adjusted map control styling