exposure export tool: client export enhancements

There are a few client side enhancements that can make for a much better user experience.

    * Add a heads-up display of the lat and long of the current mouse position. In this way the user will be able to make a more informed selection
    * Add a heads-up display of the area being selected in the bounding box. If possible change the font from black to red when the max size allowed is exceeded
    * Add a loading wheel to the exposure export dialog download button: once the button is clicked the loading wheel should be fired, then some feedback logic that prevents the user from inadvertently downloading multiple times
    * Update the help hover text
    * Clean up the arrangement of map controls; the selection tool box gets moved when you mouse over the layer selection
    * When the selection tool is clicked, there should be some feedback on the tool itself that selection mode is enabled. This could something as simple as putting a checkmark in the box for the selection tool.