Determine a namespace system for component names

[jlowin]

Most Prefab components are known at compile time and can be assigned or given names. However, some arrive at runtime and are inserted into <Slot> components. These could potentially have names (and therefore reactive state) that clobber existing variables - in fact, if generated from the Python DSL, they almost certainly will, as the counter may have reset.

Therefore, we should consider:

1. namespacing for component names, to ensure that collisions don't happen outside local scope. This is naturally appealing but has potential downsides that hardcoded component references may have to know their parent component or scope
2. uuids (or uuid-8) instead of counters, to reduce the probability of global collision
3. something else?