change location of "static" ensight geometry

Looking at adding in multi-region support for foamToEnsight (#2080 (closed)) and we have a slight chance of name collisions if someone happens to have a region called "data" or "geometry", since these are reserved names in our EnSight output.

Was thinking that geometry should become data/constant/geometry, by inserting a constant data sub-directory.

Any concerns about this affecting workflows etc, or any other thoughts?