enhance wcs-client with map drop down

[Vlad Merticariu]

The task is to add a section similar to Avaialble coverages on the first page of the client. It should contain a map displaying rectangles which represent the extents of the available coverages, which can be extracted from the coverage description (check the describe coverage tab for an example).

On hovering over a rectangle, a tooltip showing the name and extent of the coverage should be displayed.

Please use the openlayers library for this, you can find a lot of examples on how to draw shapes and add tooltips here: ​http://openlayers.org/en/latest/examples/