Support partitioned cmesh creation without ghost layer

[lenaploetzke]

Feature request

Is your feature request related to a problem? Please describe.

If a partitioned cmesh is created, e.g., with
t8_cmesh_new_hypercube (T8_ECLASS_TET, comm, 0, 1, 0);
the cmesh is always created with a ghost layer.
For forests, we do not include a ghost layer per default.

Describe the solution or feature you'd like

We should discuss whether we need the ghost layer by default. Perhaps an additional option to switch off the ghost layer would be sufficient.

Estimated priority

"Priority: low" Should be solved eventually
(or even very low)