Reorganize externalNORSERun.py sections into functions

[olaszsoma]

Many parts of externalNORSERun.py are coherent sections, which could be moved to separate functions altogether. This reorganization has to be done before release.

[olaszsoma]

The interface will be organized into an object, which will call the Matlab NORSE program. This will have to be done later.

[olaszsoma]

This issue will be postponed, it will be removed from NORSE release 1.0.0.