Add object registry

[DaveBerkeley]

It is useful to be able to store objects in a common place where they can be retrieved by name.

For example, if there is an I2C interface required by other components, they can request if from the registry by name.

This reduces coupling between classes, avoids app specific globals and allows unit test environments to be written in a flexible, portable way.

[DaveBerkeley]

Done https://github.com/DaveBerkeley/panglos/blob/master/src/object.cpp