templatectl: Add/Remove items from templates.json via cli

[PeterGrace]

(Re-open of PR #221 with proper branch targeting.)

This PR adds a package file for templatectl, which is a rust-based binary that interacts with the /usr/share/remarkable/templates/templates.json file. It can add entries and remove entries from the file, sparing the end user the need to edit the json file manually.

Additionally, since it is a cli-based app and will be installable via toltec, we can then use it to package template files in toltec for installing to xochitl from the package repository.

[LinusCDE]

works like a charm 👍

[matteodelabre]

Thanks for your PR @PeterGrace! Here are a few comments.

[Eeems]

Deferring system upgrade question until we handle #109

[Eeems]

@matteodelabre I think this is ready to merge, but I'd like you to double check my changes.

Changes done.

[matteodelabre]

This looks good. Going to test this on my device and will report back with comments. Here are some notes on the diff:

[matteodelabre]

Tested on rM1, works great! As might be expected, I had to restart xochitl to make the templates appear, this might confuse users as it’s not explicitly mentioned in the install output.

[Eeems]

Tested on rM1, works great! As might be expected, I had to restart xochitl to make the templates appear, this might confuse users as it’s not explicitly mentioned in the install output.

Perhaps that's something templatectl should be in charge of outputting if it detects that xochitl is runing?