Make Postorius more usable without Javascript

This issue will track all parts of Postorius that rely on javascript support and add extra elements/modify them to work at a basic level without javascript.

• Dropdown from the nav bar doesn't work without JS
• Dropdown in the list index page to filter by role doesn't work without JS
• Dropdowns in the list navigation
  • Subscriptions
  • Mass operations
  • Users
• Held message modal