Allow for the xpath to begin with 'MorpheusModel' in addition to '.'

Why?

As of now, only xpaths starting with '.' can be processed by fmc, for example "./CellTypes/CellType/System/Constant[@symbol='V1']". However, in newer versions, Morpheus exports the xpaths as "MorpheusModel/CellTypes/CellType/System/Constant[@symbol='V1']". This leads to fmc failing with the error message: "par_map['V1'] should be a str or a list/tuple of length 2". Which is in this special case not informative enough to point the user to the easy fix.

How?

Since python's xml library is not able to find files with this new version of the xpath, I opted for the simple solution of just doing a substring replacement where necessary.

How was the change tested?

Apart from test runs on my machine, I added a unit test to confirm that both reading from the xml file and writing to it works with the new format.

What else?

I added a few entries to the .gitignore.