Split the UI into more separate files and functionality

[klattimer]

No description provided.

[klattimer]

This is sort of in progress, the hard part at the minute is how we decide the toplevel links and give them data required - for instance the diskio plugin wants to be in the disk section, but so do other plugins. Which one takes ownership of creating the toplevel so that the plugins can define their own toplevels. Or do we have a standard set of toplevels and allow plugins to create their own toplevels. I think the second option is more viable.