[For 1.8] MyConversations: a conversation plugin for MyBB

[Laird]

MyConversations version 1.2.7 has just been released (1.2.6 was not released publicly).

New features:

• Resolves even more PHP 8 warnings and any minor bugs they indicated.
  
• Bugfix: The collapse/expand functionality in the UserCP left sidebar menu was broken.
  
• Bugfix: Messages hard-deleted by a member were showing up in his/her search results.
  
• Bugfix: {$cnv_ucp_options} was not being removed from the usercp_options template on plugin deactivation.
  
• Bugfix: The incorrect redirect function was called when clicking "No" at the uninstallation warning.
  
• Bugfix: When participants were removed from a group, they were not removed from group conversations in which their rights had been customised.
  
• Bugfix: The database table prefix was hard-coded to the default mybb_ in some generated SQL.
  
• Adds admin logging of the migration procedures.
  
• Adds better redirection from "Send PM" links: now, they link to the conversation-starting form with the member in question as a pre-filled recipient.
  
• Improves the presentation of member profile contact details: sometimes, they weren't shown when they ought to have been, and, even when MyConversations was active, the link to send a PM was shown.
  
• Adds better handling of absolute paths when removing attachment files and directories.
  
• Fixes some hook parameters.
  
• Reduces the length of the key on the attachname column of the attachments table for broader MySQL/MariaDB compatibility.
  
• Improves and hardens error-handling around folder IDs and names.
  
• Makes various other minor improvements and resolves various other minor issues/bugs.
  

A big thanks to @HLFadmin for his help in identifying and resolving issues.