Major overhaul of Manager vs Configuration API and much more

This pre-release is a major overhaul the Manager vs Configuration API; the WithNodeList, WithNodeMap and WithNodeIDs have been moved out of Manager and now is passed to Configuration at creation time. Further, what needs to be generated has been reduced even further, moving more logic to the top-level gorums package. Also, less info needs to be passed to the various call types (Call Data). Further, the documentation has been updated. The unused gorums.ordered option has been removed. Fixes an with PerNodeArgFunc and adds proper tests for this. And much more. See the commit messages and PR descriptions for additional details.