#2: remaining elements

[nwilging]

Closes #2

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Remaining Elements:

• [x] Multi Selects:
  • [x] Conversations
  • [x] External Source
  • [x] Public channels
  • [x] Users
• [x] Image
• [x] Overflow menu
• [x] Plain Text Input
• [x] Radio button group
• [x] Select menus:
  • [x] Static options
  • [x] External source
  • [x] Users
  • [x] Conversations
  • [x] Public channels
• [x] Time picker