Private Messages: Sent and Custom Folders

[dfsm]

Adding "Sent" folder and custom folders in private messages, enabling users to:

• View sent messages
• Create and manage custom folders
• Move messages between folders (including bulk operations)
• Delete multiple messages at once

Key Changes:

• New Folder System: Added PrivateMessageFolder Core Data entity to track folders (Inbox, Sent, Custom)
• Folder Picker UI: Segmented control for switching between Inbox/Sent/Custom folders
• Folder Management: New management screen for creating/deleting custom folders
• Bulk Operations: Edit mode with multi-select for moving/deleting multiple messages
• Sent Messages Display: Shows "To: username" for sent messages with appropriate icons
• API Support: Added ForumsClient methods for folder CRUD operations and message movement

Fixes:

• Avatars now visible in messages

• character no longer scraped and then added to reply message titles