Pre-test rules before running a simulation

[rafaqz]

Before running any simulation we should run all rules once in a contained environment and give sensible errors/warnings for any problems with them. Instead of having them buried in the middle of a complicated optimisations of the simulation as they are currently.

1. make sure rules have the correct output types if they have output.
2. make sure rules only access existing Aux and Grid data. Probably we can do this with AST analysis of the applyrule function.
3. Check anonymous functions for boxed variables and warn/error
4. we can run rules on the max and min values present in their init grids, and stencils from the locations of these values for neighborhoods.
5. test type stability and inference by default, but only throw a warning if it is lacking.

We also need a flag to turn this off.