Layout update for NanoUI.

The layout HTML (which was mainly used for the title bar) is no longer hard coded in nanoui.dm.
Layouts are now dynamic and each consists of a template and stylesheet (CSS) file.
Multiple layouts can exist, they can be switched to using the set_layout_key proc. See the proc comments for more info.
Added "default" and "basic" layouts, "basic" has no title bar.
Moved image source assets (GIMP and Flash files) into a separate source folder so that they are not sent to the client.