Add import/export CSV or XML file

[MickCZ]

Adding import/export option for each category of filament, manufacturer, spools e.g. in CSV or XML file for further processing options in MS Excel etc.
Many manufacturers allow downloading CSV files of their entire production including barcodes which would make it easier to import into Spoolman after editing in an external spreadsheet program.

[vladimir-poleh]

There is a #193 PR with export to CSV implementation. Please wait for merge.

[napalmz]

There is a #193 PR with export to CSV implementation. Please wait for merge.

PR #193 is for EXPORT, we also need and IMPORT.
I've 2 deployment of Spoolman and I want to update one from another using export->import.

Thank you

[vladimir-poleh]

How are you planning to match spools between Spoolman instances? It is possible that same ID will be used for different spools.
The correct way is a single Spoolman instance shared between locations.

[napalmz]

The concept of "unique key" has to be considered besides the presence of ad unique ID.
I should not insert an identical vendor/filament/spool which difference only by id, it'll make no sense.
Import should check if an unique key (composed of relevant fields) is present and if yes, use this ID instead during import.