Bootstrap upgraded to 5.0.2

[rg663]

Fixes #436 — ColdFront now uses Bootstrap 5.0.2 instead of 4.6.1.

Detailed updates:

• syntax migrations have been made throughout, so all buttons and links function as they should (for example, Bootstrap 5 drops .badge-* color classes and uses .bg-* instead)
• the default date and datetime formats have been changed in base.py, so now they appear consistently throughout the interface

• DATE_FORMAT = 'Y-m-d' (example: 2022-08-09)
• DATETIME_FORMAT = 'Y-m-d H:i' (example: 2022-08-09 14:02)

• with Bootstrap 5, checkboxes have a new look, but it is inconsistent with how some of the other checkboxes on the website that inherited crispy-forms are formatted, so the CSS is overridden to match these
• Bootstrap 5 links are underlined by default, so the CSS is also overridden to remove this underline
• small tweaks were made throughout, such as removing the bullet points that appeared on error messages, adding spaces and padding, etc.
• crispy-bootstrap5 is added to allow for future editing in crispy-forms using new Bootstrap 5 features