Changes

Fix principia multi-node

The node executor now works with two maneuvers planned.

The button for multi-node shows up.

There's a bug that I don't know how to fix because there's at least
one tick between the last maneuver node disappearing and the next
maneuver node showing up.  So the multi-node executor sees no future
nodes, so it quits.

Signed-off-by: Lamont Granquist <lamont@scriptkiddie.org>
 (commit: e21bb53)