Improve Singe- and MultiGridClosure to skip in case first seeds; always give return 0 for force = True

Implemented channel dependent multi_channel setting in NNLOJET runcard; implemented channel dependent setting of OMP threads for NNLOJET(use_cpus); missing: channel dependent no. of CPUs to request in htcondor config (request_cpus)

Numerous changes to fix issues from transition to NNLOJET modules2; added actual luigi/law configs as templates; added CMS7TeV dijet setup as example runcard and steering

Update law to `v0.1.12`, reduction of code duplication, and various small fixes.

See merge request !6