Spatial: clarify/comment in scope about dynamics of spatial objects

[matthiaskoenig]

I realized thinking about spatial and spatial problems I have that the current spatial specification is limited to static spatial descriptions. This is a major limitation of the specification and should be clearly stated/explained in the scope (similar to explanation for distrib that multi-dimensional distributions are out of scope).

Most biological systems change in their spatial geometry over time, e.g. cells move, tissue deforms, vesicles and cells change size and form. Such changes are currently not possible with spatial but it is limited to using a static geometry and perform simulation in the geometry. It is important to clearly state this early in the specification, so that users who require temporal dynamics of the geometry are not disappointed.