[Handshake] Use symbols instead of id integer attributes for memories

[mortbopet]

All handshake memories must currently have an id integer attribute. To no surprise, this is used to unique each handshake memory.
Issues with this:

1. No logic is implemented to assert that id's are actually unique
2. The ids should be replaced with symbols (in other words, memories should be named). This will also help lowerings, which nevertheless are forced to come up with some unique name for the memory (currently based on the id).