Docs update

[jj0hns0n]

Some serious editing in the user section of the docs, and added heaps of screenshots to illustrate the various bits of the documentation.

[dwins]

This picture: https://github.com/jj0hns0n/geonode/blob/e15b28608a76296e7444b5dc505c37a3d337afab/docs/users/images/download_map.png

demonstrates a giant bug (notice how ALL THE LAYERS IN THE MAP are listed as ones that will be excluded because they are not internal layers to the GeoNode.) I don't think it makes a lot of sense to document this buggy behavior, or at least we should be documenting that the "download all the layers in this map" functionality doesn't work instead of instructing users to use it.

[jj0hns0n]

Yep, I noticed this yesterday and made a note to replace the graphic once its fixed. There are also a few other things like this. My feeling is that this is a problem of the databases being out sync on the demo server since there are other places like the Map Detail page that think the layers are somehow not local.