Rename file

Rename `symoroui/gui.py` to `symoroui/layout.py` and update accordingly.
Move `parfile` module

Move `pysymoro/parfile.py` to `symoroutils/parfile.py` and update module
importing accordingly.
Create `symoroutils/filemgr.py` file

Create `symoroutils/filemgr.py` file.
Move file management functions to this new file.
Update function calls in appropriate places.