Feature/blocklevel detection

Proposal for extending !168 (closed) to MultiTypeBlockMatrix. As the blockLevel for MultiTypeBlockMatrix is sometimes not uniquely determined this proposed three functions minBlockLevel, maxBlockLevel and blockLevel. The first two always work. The last one is only enabled if the first two return equal levels. There is an additional function constexpr bool hasUniqueBlockLevel() which checks this condition at compile time.

Depends on the fix in hybrid utilities dune-common!794 (merged)