Limited movement

[rusu24edward]

Agent movement is currently only restricted by the presence of non-overlappable agents. We want to support other kinds of restriction, such as:

1. Available region by encoding in the grid. Support movement region by encoding #513
   1. Observer showing available region
   2. Could consider moving the available region (e.g. must be within some distance of another agent). But not clear what happens when the agent falls outside of this region. Does it die? Does it become immobile until its "partner" returns? This is too detailed, and should be up to the designer. We just want to support available regions/cells.
2. Movement gas, when run out the agent cannot move anymore. Movement gas #514