Improve issue search (#2387)

* Improve issue indexer

* Fix new issue sqlite bug

* Different test indexer paths for each db

* Add integration indexer paths to make clean

routers/repo/issue.go

@@ -22,6 +22,7 @@ import (
 	"code.gitea.io/gitea/modules/auth"
 	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/context"
+	"code.gitea.io/gitea/modules/indexer"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/markdown"
 	"code.gitea.io/gitea/modules/notification"
@@ -142,7 +143,7 @@ func Issues(ctx *context.Context) {
 	var issueIDs []int64
 	var err error
 	if len(keyword) > 0 {
-		issueIDs, err = models.SearchIssuesByKeyword(repo.ID, keyword)
+		issueIDs, err = indexer.SearchIssuesByKeyword(repo.ID, keyword)
 		if len(issueIDs) == 0 {
 			forceEmpty = true
 		}