added File->Clear + changed behaviour of File->New (now just adds a
new model)

allow smaller fonts for palettes (test with "-deltafontsize")

use display list for 3d arrows (approx. 2x speedup on my laptop for
large vector views) and spheres

removed static quadrics (wrong when \exists multiple gl contexts),
replaced with correct(?) init in drawContext

- fix bb computation to avoid model jumping around when adding points in z=0 plane
- pass interpol matrices as ref

Third phase of code refactoring: move callbacks where they belong
& drastically reduce namespace pollution.

There's no new functionality for now: PLEASE TEST THAT EVERYTHING
WORKS AS IT USED TO BEFORE.

There's no new functionality for now: PLEASE TEST THAT EVERYTHING
WORKS AS IT USED TO BEFORE.