Implement remaining network methods for networkLite if necessary.

They are:

- [ ] `get.edgeIDs()`
- [ ] `get.edges()`
- [ ] `get.dyads.eids()`
- [ ] `get.inducedSubgraph()`
- [ ] `get.neighborhood()`
- [ ] `is.adjacent()`
- [ ] `network.density()`
- [ ] `has.edges()`

Some of them may work out of the box, particularly if they do not depend on `network`'s internal structure.