Remove/replace deprecated functions django 3

Update Django to 2.1.15.

Order round admin by end date by default.

Add a open/closed filter to the round admin page in wagtail admin.

Add flag feature to allow staff as well as each users to flag submiss…

Use FileResponse as in Django 2.1 it tries to set the Content-Type, Content-Length headers

Admin: Create copy button in Application form

Make big tables and long links etc fit within the layout

Updating roadmap link and other in the readme.

Fix to Automatic workflow actions after creating seperate view for re…

Set TIME_ZONE to UTC to avoid summertime.

Add index on source_object_id for 10x performance improvment on orderBy

Set postgres version to 10.10 in CI as it is on production.

[Security] Bump werkzeug from 0.14.1 to 0.15.3

Bumps [werkzeug](https://github.com/pallets/werkzeug) from 0.14.1 to 0.15.3. **This update includes a security fix.**
- [Release notes](https://github.com/pallets/werkzeug/releases)
- [Changelog](https://github.com/pallets/werkzeug/blob/master/CHANGES.rst)
- [Commits](https://github.com/pallets/werkzeug/compare/0.14.1...0.15.3

)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

* User reportlab to render the submissions into pdf

* Improve layout and look of submissions and pdfs
This makes headings render smaller than the questions within rich text fields

* Enable h1 tag in bleach
Based on changes to how headings are rendered this is now more reasonable.

Remove the global activity feed. No one is using it so lets save some…

Allow staff to see 16 reviewers in the reviewers field, before only f…

Fix the creation of files under the submission's revision path 

Remove get_field_kwargs() in ImageFieldBlock. We do not need this whe…

Reduce DB queries for Table data

Add Debug Toolbar to Dev