Allowed robot to fire "rockets"

They're mostly here to test object-motion performance.
They start out very fast, but they have some friction
   and they random-walk a bit.
Merge branch 'master' of https://github.com/elidupree/Lasercake
Bugfix: Restrict global-view-navigation keys to global view mode.
UI improvement: make global view navigation continuous not per-keypress

This brings its behavior in alignment with local view navigation
(and robot navigation). Change approved by Eli.
improve key choices somewhat
refactor robot turnleft/turnright
fix robot pick up/drop rubble (but still don't document it)

Don't document it because it still isn't a very practical interface;
it's kind of tedious *and* it's hard to be precise about which
rock you're picking up.
Change local-view navigation to be mostly in line with robot navigation.
Merge branch 'rekeying'