Add fast-forward and speed slider to debugReactiveOf.
Add fast-forward and speed slider to debugReactiveOf.

This completes the process of adding debug controls to native
reflex programs.  All further debug controls rely on assumptions
about the state, and so must be implemented in the transition
layer before reaching reflex.

Fixes #1038

alphalambda/codeworld,google/codeworld,alphalambda/codeworld,google/codeworld,google/codeworld,alphalambda/codeworld