Autotag optimisation (#2368)

* Add duration to autotag finish message
* No sorting scene/image/gallery where not specified
* Use an LRU cache for sqlite regexp function
* Compile path separator regex once
* Cache objects with single letter first names
* Move finished auto-tag log
* Add more verbose logging
* Add new changelog

pkg/database/functions.go

@@ -1,15 +1,10 @@
 package database
 
 import (
-	"regexp"
 	"strconv"
 	"strings"
 )
 
-func regexFn(re, s string) (bool, error) {
-	return regexp.MatchString(re, s)
-}
-
 func durationToTinyIntFn(str string) (int64, error) {
 	splits := strings.Split(str, ":")