Conversation Improvements by Xon 2.5.1

• Fix that the conversation starter was not included into the allowed list of users when searching for conversations.
  • Will need to rebuild the search index for Conversations and Conversation Messages.

• Fix migration process for legacy leftover XF1 columns

• Harden installer to handle legacy leftover XF1 columns

• Rework installer to be more robust.
  • Ensure the src/addons/SV/Utils folder is also uploaded! If it exists, just overwrite.

• Convert XF1 columns (for xf_conversation_master table) to XF2 names on upgrade where required