Contacts UI improvements

Honestly the UI just needs to be standardized for the pages dealing with Contacts, here’s some priority-ordered suggestions. Standard table components with hideable columns & user-selectable filters & sorts are widely available, it’d make things much easier if the table views used something like that.

• Single-Contact view: show Created At & datetime timezone

  • /contacts/{id}/details

  • already shows Last Updated but timezone is unclear

  • Created At is available via API, just needs display

• Segments view: add filters, columns, actions, & pagination

  • /contacts/segments/{id}

  • add filters for Last Updated & Subscribed

  • add Subscribed column

  • add Download action

  • add pagination