disable crons and workers which do nothing

[pbiggar]

When saving any handler or function, mark if it does anything (if everything it calls is non-side-effecting).

This should be saved in the toplevel_oplist table. When loading crons and workers, don't do anything if it's impure. Perhaps they shouldn't be emit (unless it's paused) or else they shouldn't run if they're ready to load.

[StachuDotNet]

folding this into a larger issue shortly