Change node id generation to give fixed length values without '.'

[knolleary]

Proposed changes

This PR changes the algorithm used to generate ids in the editor and runtime.

The existing code could produce variable length ids and had a . in the middle - which was accidental rather than intentional because all those years ago, I forgot to include Math.floor() in the code. eg bfc71766.923608

The new algorithm creates 8-byte fixed length ids without the . - eg 4ab59dd6503989b6. This gives us a range of 2^64 − 1 values - which is suitably random to avoid collisions within individual NR instances.

[coveralls]

Coverage increased (+0.007%) to 67.653% when pulling 8bbed2c on clean-ids into 6b43a23 on dev.