Add admin form for new event

[differentreality]

Checklist

• [x] I have read the Contribution & Best practices Guide.
• [x] My branch is up-to-date with the upstream master branch.
• [ ] The tests pass locally with my changes.
• [ ] I have added tests that prove my fix is effective or that my feature works(if appropriate).
• [ ] I have added necessary documentation (if appropriate).

Short description of what this resolves/which issues does this fix?:

• Provide a form for admins to add a new event

Changes proposed in this pull request:

• Use the proposals/form to render the form for admins

[AndrewKvalheim]

Thoughts on #3073?

[differentreality]

Yeah that works for the admin/events form, I'd have to take a closer look at the rest of the changes it introduces

[AndrewKvalheim]

For reference, a comparison with the previous form:

Previous (3bbbdb4)	Proposed (9819984)