Bootstrap upgraded to 5.3.0

[rg663]

Resolves #436 — Now, ColdFront uses Bootstrap 5.3.0 instead of 4.6.1.

Detailed updates:

• Users can now enable dark mode by toggling the option in their User Profile menu.
• Colors, date formats, and alignments have been updated throughout.
• Crispy-bootstrap5 package is installed for anyone who wants to add additional Bootstrap 5 functionality.

For anyone updating to this version of ColdFront, be sure to run coldfront collectstatic to migrate all static updates.