MatPipe.load should refuse to load from class instance

[ardunn]

MatPipe load should not work if the pipe was previously defined in an instance. It should only work as a static/classmethod usage, not as an instance usage. This is because it is more reliable to load and define matpipes entirely at one time rather than mixing and matching constituent classes through __init__ and __load__

Good:

MatPipe.load(file)

Bad:

pipe = MatPipe(**some_config)
pipe.load(file)