remove hard constraint on context arg in Frankenstein class

[pdmct]

This removes the hard constraint on the Frankenstein class.
It checks for the presence of "context" before using it to get the implementations, thus allowing a component to be created without the context (if so desired).

This is necessary to get some experiments with basilisp working among other things (and shouldn't affect any existing functionality), as the context is required to be a positional arg in the constructor to avoid name munging difficulties.