feat: show signature status on files app

[vitormattos]

Pull Request Description

This pull request adds an icon to the right of the files, in the files app, showing the file signature status on the original and the signed files. The original will have the status 'Original file signed elsewhere' and the signed file will have the status 'Partially signed' and 'Signed', depending on the signing progress.

Before:	After:

To test the feature, after checking out to the pull request:

• upload a PDF file to Nextcloud using the files app;
• request the signature from two different users;
• sign the file with one of the requested users;
• the original file will show a green sign icon, with the text 'original file' when hovering over it;
• the signed file will show a yellow ½ icon, with the text 'partially signed' when hovering over it;
• now sign the file with the second requested user;
• the signed file will show a blue sign icon, with the text 'signed' when hovering over it.

Related Issue

Issue Number: #4160

Pull Request Type

• Feature

Pull request checklist

• Did you explain or provide a way of how can we test your code ?
• If your pull request is related to frontend modifications provide a print of before and after screen
• Did you provide a general summary of your changes ?
• Try to limit your pull request to one type, submit multiple pull requests if needed
• I implemented tests that cover my contribution