SAK-49082 DateManager improvements to additional nullable date support

[mylescarey2019]

This pull request adds UX features to Date Manager and fixes several open issues.
Fixed are the following:
From the re-opened SAK-46023 - Date Manager > Nullable fields for some activities needs to be allowed

• Tests & Quizzes hide feedback date - No error, but no change in the settings. When you reload date manager, these dates re-appear
• Announcements start/end dates - “Uncaught Error” in Date Manager when trying to save after clearing out dates
• Lessons hide until date- “Uncaught Error” in Date Manager when trying to save after clearing out dates

Also fixed:

• SAK-46212 - Date Manager: unable to change announcement dates if open date set without hide date
• SAK-48788 - Date Manager: Announcements - Uncaught error (SQL lock) if fixing date from previous error
• SAK-48789 - Date Manager: Calendar - Uncaught error (SQL lock) if fixing date from previous error
• Resources affecting Files (not Folders): Uncaught error (SQL lock) if fixing date from previous error

UX Features added to Date Manager:

• Ability to clear any date - required date fields subject to validation upon Save
• Assessible Clear date button
• Date input field value now shows in title element (helpful for Accessibility and when dates fields compressed due to narrow screen widths (tablets, etc.)

[ern]

@mylescarey2019 Thank you for the PR

In the future you should only mention the JIRA that this PR is for, you can mention any other related JIRA issues in the JIRA ticket.