Module table improvements 3: offload storage to LMDB

[td202]

Since the set of modules only grows, it would make sense to move all module data into the LMDB database, instead of the block state. Alternatively, just the module source could be kept in the block state, and the compiled artifact and metadata could be retained in the LMDB database. This would reduce the amount of data that needs to be copied on protocol updates. This is probably more pertinent in the context of a light node, if we continually roll the block state database, as it avoids having to roll the modules as part of that.