Files (and folders) are still slugified to ASCII for storage on disk,
but now the original filename is stored alongside in metadata.yaml
and used for display in the file list and print status.
The slicing dialog also inherits that display name for use as base
for the suggested GCODE name.
Internally, everything still depends completely on the slugified
ASCII version.
This implements #2094
On MacOS, `tempfile.mkdtemp()` doesn't necessarily return a canonical
path (it uses `/private/var` instead of `/var`, but they are the same
thing). Since the `filemanager.storage` module canonicalizes paths,
tests were erroneously failing due to prefix match failures.
- File management is prepared to support folders (UI still lacking support)
- STL files are now first class citizens
- can be managed via the file list (and filtered from it)
- can be sliced on demand
- Slicing now happens via plugins
- Added Cura plugin
- uses CuraEngine directly instead of full Cura installation
- Cura profile importer for importing profiles from regular Cura installs via settings dialog
- TODO: UI for editing profiles
- API for slicing and slicing profile management
