Username auto-complete using XFES 1.5.0

• Require StandardLib v1.19.0+
• Require Search Improvements 2.12.0+
• Fix admincp quick search could potentially return the same user multiple times

• Fix moving a user in/out of a group which blocks mentions didn't force visibility for mentions to be updated
• Fix indexing queue for pushing user last activity into the search index could skip users
• Workaround edge case where a user's with very old last activity record could be updated but was not pushed into the search index

• Fix duplicate exponential decay being added for username autocomplete (did not appear to affect results)
  If using Search Improvements v2.11.0+, Username autocomplete now prefers prefix matches
  • Recommend updating Search Improvements to v2.11.0+

• Require Standard Library by Xon v1.18.0+
• Add "Block mentions for members of group(s)" option.
  • Removed from front-end user auto-complete
  • Prevents mentioning from sending mention/quote alerts