Read-structure-step

* Fixed a bug that caused a crash when reading MOPAC files with references in the
comments.
* Updated the MOPAC reader to the new approach for running MOPAC in the cases that
it is needed: Z-matrices and mixed inputs that OpenBabel can't handle.

* Changed the handling of paths to make them relative to the directory that the step
is running in. In a loop, for instance, files are relative to the iteration
directory.
* When reading files, allow the syntax 'job://<job number>/...' to read files from
another job. If the job number is omitted, so the prefix is 'job:///...', the top
directory of the current job is used.

* Made the naming of systems and configurations consistent with the standard
parameters for them in the GUI.
* Removed all "from file" options, replacing them with "title", which means the title
from the file, if it exists, or the filename if it doesn't.

* Crashed reading some SDF files write by SEAMM due to the system and configuration
names encoded in the title having multiple slashes (/).

2023.11.5 -- Added writers for CIF and mmCIF.

* Moving towards the standard structure handling that has developed across SEAMM.

2023.7.28 -- Implemented ranges for reading XYZ and SDF files.

2023.7.27.1 -- Removed debug printing.