Add feedback button

[Splines]

New feedback button for users to give feedback regarding MaMpf. Closes #466

⚠ Merge #537 beforehand, then bring in mampf-next into this branch.

TODOs

• Prevent sending feedback with empty message
• Make sure everything works when title is empty (title is optional)
• Implement better user flow: close modal and clear message upon successful sending, otherwise show flash error message.
• Set FEEDBACK_EMAIL env variable in production! -> won't be reflected in this PR, manual in production environment
• Test email delivery in experimental.

Preview

For reviewers

• Check internationalization: everything should work fine in German as well as English including
  • all the texts in the modal
  • success/error toast messages
• Check user flow
  • good path: write feedback and submit, check in Mailcatcher if email arrived
  • error paths: write feedback with no characters, in app/controllers/FeedbacksController inside the create method, add: @feedback_success = false right before respond_to(&:js) to simulate unsuccessful saving of message to database, simulate bad internet connection, other error paths?
• Code quality & linting!
• Check that "Allow us to contact you via email" is correctly reflected in Reply-to of mail (only if checkbox is ticked should we be able to contact the user by replying to the mail, otherwise Reply-to field should be empty)
• Clean state: after having successfully submitted feedback, modal should close and next time have texts cleared. If error: modal should stay open and text should not be cleared. Text should also not be cleared when user writes feedback, closes modal (without submitting), then opens it again.
• Mobile: test that feedback submit button is still visible in navbar.
• Own ideas to test this feature: ... (specify)

[codecov]

Codecov Report

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Additional details and impacted files

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[Splines]

Hey @Frodo161, this PR is now ready for your review ;) Please see the For reviewers section in my upmost comment here. You can tick off the checklist there and also edit my comment.

[Frodo161]

Problems:

• "Bitte verwenden Sie zumindest 10 Zeichen" is in German even if the language is set to English.
• If one uses "@feedback_sucess = false" as described in the PR, nothing happens (only the modal won't close on save). Especially, there is no error message (should there be one?). The mail arrives in the mail catcher as expected.
• More generally, I didn't get to see any of the error messages that are written down in the locale files.

Code:

• Maybe, instead of writing authorize_resource except: [:create] in the FeedbacksController, you can add an ability file for feedback.

[fosterfarrell9]

Looks good to me. Before merging into production: Has this

• Set FEEDBACK_EMAIL env variable in production! -> won't be reflected in this PR, manual in production environment

been done yet?

The base branch was changed.

[Splines]

Will merge without approval as Denis is on vacation.