Switch from pointers to IDs

Switch from pointers to IDs

Mosfets holding pointers to nodes (and nodes to mosfets) causes problems
when the nodes (or mosfets) vector reallocates. The reallocation
invalidates any pointers.
Holding the ID prevents the invalidation, but may cause performance
issues as the vector needs to be searched for the ID (binary search
would help and is applicable).
The IDs also make the code more networked, because the nodes and mosfets
vectors need to be passed to many more functions.