Change default windows manager to lxde

[WardF]

The default Windows manager is currently fluxbox. It is functional and lightweight, but not the easiest to use. I think the default should be lxde, as seen in the Linux Desktop example. This will also require modifying the CloudIDV project, and CloudIDV example, to overwrite the default lxde desktop to switch back to fluxbox, if we want. This will be driven primarily by final docker image size.

[WardF]

Dropping this change; it more than doubles the size of the unidata/cloudstream docker images (from 430MB to 954MB). This is unfortunate, but we'll maintain the lightweight version even though it's not quite as nice. We'll investigate other lightweight windows managers, like Ratpoison.