Bugfix and reimplement Pictrs

[Gildas-GH]

Problem

The current package in master has three problems :

• It is not up to date with upstream
• It is broken due to an error with Sharp
• It doesn't support image upload

Solution

• The first problem cannot be solved as the PostgreSQL version available in Bullseye doesn't meet the requirements of Lemmy. We have to wait.
• The two other can be solved with #43 and a bugfix contained in this branch

PR Status

• [x] Code finished and ready to be reviewed/tested
• [x] The fix/enhancement were manually tested (if applicable)

Automatic tests

Automatic tests can be triggered on https://ci-apps-dev.yunohost.org/ after creating the PR, by commenting "!testme", "!gogogadgetoci" or "By the power of systemd, I invoke The Great App CI to test this Pull Request!". (N.B. : for this to work you need to be a member of the Yunohost-Apps organization)

[ericgaspar]

!testme

[yunohost-bot]

Alrighty!