Added CLI Interface

[Viermusketiere]

I added a CLI interface which enables the plugin to be used standalone on an arbitrary board file.
Reason is that most other JLCPCB scripts available either require a schematic file (which in my case is not available).

No additional dependencies are added.
Changes to existing code have been kept to a bare minimum as the plugin functionality is the main feature.

CLI can simply be used by cloning the repository and running python -m plugins.cli -p [pathToBoardFile].
See python -m plugins.cli --help on how to set all options which are implemented in the GUI menu as command parameters.

python3 -m plugins.cli -h

usage: Fabrication Toolkit [-h] --path PATH [--additionalLayers ADDITIONALLAYERS] [--user1VCut] [--user2AltVCut] [--autoTransitions] [--autoFill] [--excludeDNP] [--openBrowser]

Generates JLCPCB production files from a KiCAD board file

options:
  -h, --help            show this help message and exit
  --path PATH, -p PATH  Path to KiCAD board file
  --additionalLayers ADDITIONALLAYERS, -aL ADDITIONALLAYERS  Additional layers(comma-separated)
  --user1VCut, -u1      Set User.1 as V-Cut layer
  --user2AltVCut, -u2   Use User.2 for alternative Edge-Cut layer
  --autoTransitions, -t    Apply automatic position/rotation translations
  --autoFill, -f        Apply automatic fill for all zones
  --excludeDNP, -e      Exclude DNP components from BOM
  --openBrowser, -b     Open webbrowser with directory file overview after generation

Feel free to make any suggestion on improvements.