new UI and refactor/split revert/fork

can't yet fork one's own but it's almost structured right
error objects for decent reporting
hide optional icons until loaded

save/revert were distracting me
centralize load logic
very clever sequential numbering of copies/forks

which happens to work exactly like on OSX
basic forking of own notebook, without history

want to get the UI right, first
Merge branch 'develop' of https://github.com/att/rcloud into develop