xF2 Add-on User Mentions Improvements by Xon 2.10.1

• Prevent erroring when User Essentials is rebuilding user mentions and a post without a thread is encountered.

• Fix a memory leak when running from a long running process (effects User Essential's mention tracking rebuild)

• Fix typo in email footers

• Fix "Undefined index: sv_email_on_quote" by installing default registration settings on upgrade instead of just install.

• Actually apply user registration defaults on account creation
• Require XF 2.0.4+

• Allow extra email options processed by account/account-details to be saved

• Fix email preferences not showing in XF2.0.4+

• Support for User Essentials v3.0.0's advanced mention features.

• Compatibility fix for add-ons disabling mentions on creating a message
• Support for User Essentials v3.0.0

• Fix "Template error: Macro email:sv_mention_macros:quote_subject is unknown"
• Add '[UMI] View mentionable user group members' permission
  • By default granted to registered and unregistered usergroups.
  • Controls if a user group member can see the member list for public user groups
  • Global option for how completely this is hidden, by default it returns no permission. But can completely hide the user group id (returning a 404), and not render the user group mention bbcode.