[gridglueoperator]
we currently don't know how to interpolate ...
[gridglueoperator]
totally rewrite the subdomain assembly, we had to copy the code from DefaultAssembler
[test]
gridglue: instatiate the matrix and call the assemble
Revert "[gridoperator]"

This reverts commit f0a3c3ac9f1b4aae397d84d621c8c866196e82bb.
[test]
gridglue: use domain wise blocking
[test]
gridglue: initialize with 0 and print matrix, no assembly yet...