Restrict permission check on repositories and fix some problems (#5314)

* fix units permission problems

* fix some bugs and merge LoadUnits to repoAssignment

* refactor permission struct and add some copyright heads

* remove unused codes

* fix routes units check

* improve permission check

* add unit tests for permission

* fix typo

* fix tests

* fix some routes

* fix api permission check

* improve permission check

* fix some permission check

* fix tests

* fix tests

* improve some permission check

* fix some permission check

* refactor AccessLevel

* fix bug

* fix tests

* fix tests

* fix tests

* fix AccessLevel

* rename CanAccess

* fix tests

* fix comment

* fix bug

* add missing unit for test repos

* fix bug

* rename some functions

* fix routes check

routers/user/home.go

@@ -286,7 +286,12 @@ func Issues(ctx *context.Context) {
 		repo := showReposMap[repoID]
 
 		// Check if user has access to given repository.
-		if !repo.IsOwnedBy(ctxUser.ID) && !repo.HasAccess(ctxUser) {
+		perm, err := models.GetUserRepoPermission(repo, ctxUser)
+		if err != nil {
+			ctx.ServerError("GetUserRepoPermission", fmt.Errorf("[%d]%v", repoID, err))
+			return
+		}
+		if !perm.CanRead(models.UnitTypeIssues) {
 			ctx.Status(404)
 			return
 		}