Implement a generic distribution utility in the reftype framework.

This would fill a gap in communication schemes.

Note that this distribution should rely on communicators and groups.

Reference counting of sparsity patterns are needed.

The first implementation should be non-distributed sparse patterns.

Our currently intended sparse patterns are:

• CSC
• CSR
• BCSR
• BCSC

We do currently not intend to provide tools for constructing sparse patterns on the fly.
This may be useful later.