Components should always delegate to a real datatype

[jleibs]

For convenience, we currently allow components to be either:

• An inlined primitive
• A reference to a rerun datatype

Although this seemed like it would simplify creating components in cases, the net result is that components have to carry the complexity burden of both the potential to be a datatype as well as the ability to delegate through to another type.

This has resulted in plenty of code duplication, especially on the python serialization side, of re-implementing per-component support for primitives such as bool, when referencing a rerun.datatypes.bool would actually be easier.

By making all components always delegate to a concrete rerun datatype this also moves us a step in the direction of components being nothing more than a semantic label and a reference to one or more datatypes.