#4116:Display report expiration date changes

[obinnaeye]

Before you submit a pull request, please make sure:

• [x] The pull request should include a description of the problem you're trying to solve
• [x] The pull request should include overview of the suggested solution
• [x] If the pull requests changes current behavior, reasons why your solution is better.
• [x] The proposed code should be fully functional
• [ ] The proposed code should contain tests relevant to prove is functionality
• [ ] The proposed tests should ensure significative code coverage
• [ ] All new and existing tests should pass

See https://github.com/globaleaks/GlobaLeaks/issues/4116

Steps to Test Locally:

1. Checkout this branch feature/4116-display-report-expiration-changes
2. Build client code: cd client && ./node_modules/grunt/bin/grunt build
3. Start server: `cd backend && bin/globaleaks -z -n
4. Go to https://127.0.0.1:8443
5. Log into a recipient dashboard
6. Update a report expiration date
7. Confirm a new comment added to the report

Screeshots:

TODO:

Add these proposed API tests for these two endpoints: /api/recipient/rtips/{id}/comments and /api/whistleblower/wbtip/comments.

1. Assert that a comment is added for every change in expiration date.
2. Assert that the comments are visible on both the recipient's and whistleblower's reports.
3. Assert that auditlog-related comments contain all the fields, including is_audit_log and audit_log_type.

[obinnaeye]

While working on this ticket, I found a bug and have filed it https://github.com/globaleaks/GlobaLeaks/issues/4124

[evilaliv3]

Thank you @obinnaeye for your contribution!

I'm going to integrated it on top of the devel branch and perform a minor revision.