Semantically-Accurate Memlets

- [x] Memlets should not have `subset` and `other_subset`, but `src_subset` and `dst_subset` or `subset`/`reindex`
- [ ] Conversion code from relative offset to absolute offsets (a variant of memlet propagation)
- [ ] Two presentations on the renderer - relative offsets / local view (internal representation) and absolute offsets (current one we present)
- [ ] In the local view mode - access nodes have two numbers: the sum of `num_accesses` going into the node (number of inputs) and the sum of `num_accesses` going out of the node (outputs)
- [x] Connectors should have types and shapes, just like arrays
- [x] Include reference nodes (indirect access to arrays of CSR matrices, for instance)

After that:
- [ ] Transformations should be rewritten to support this new representation
- [ ] Memlet propagation is only done for the "absolute offset" view