Convert all event forms to datepicker

[mattwire]

Overview

This converts ALL event forms to datepicker:
* EventFees (On Register Event Participant for a paid event). - #12992
* Register Event Participant (Registration date) - #12979
* Event Search (On ManageEvent page - also cleaned up layout) - Before/After screenshot below. - #12978
* Manage Event - Fees - #12977
* Manage Event - Registration - #12975

Before

Event forms using old jcalendar method.

After

Event forms using new datepicker method.

Technical Details

Comments

Each form has it's own commit and can be reviewed separately if desired, but as they're all low-risk related changes (ie datepicker conversion) I think it makes sense to keep them in a single PR and whack them all in one go...

[civibot]

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[mattwire]

All now merged as separate PRs. No more datepicker in Event component :-)