Uniform spatial navigation extending into meta planes

[countvajhula]

Introduce spatial navigation of Rigpa through all referential planes -- that is, make navigation from ground to referential levels, as well as change of perspectives in referential levels, map to spatial keybindings involving hjkl, instead of relying only on Esc/Enter with modifier keys. This should retain some uniformity in changing perspectives on ground editing (e.g. Insert/Emacs mode vs Normal/Line) vs changing perspectives on a meta plane (e.g. Insert vs Line mode in editing a tower), and navigation in these different "directions" should have spatial keybindings even if they also have convenient alternatives overloading Esc.