SMS inbox refresh

The SMS inbox has been updated to make texting with customers easier to manage day to day.

• Replaced the old inbox filters with All and Unread
• Added unread indicators on conversations in the All view
• Added a Mark as unread action so you can flag a conversation for follow-up
• Added a dedicated Unread view for messages that still need a reply
• Polished the conversation thread layout for cleaner alignment
• Improved pagination with a loading indicator
• Cleaned up legacy SMS code