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

models/issue_milestone.go

@@ -377,7 +377,7 @@ func ChangeMilestoneAssign(issue *Issue, doer *User, oldMilestoneID int64) (err
 		return err
 	}
 
-	mode, _ := AccessLevel(doer.ID, issue.Repo)
+	mode, _ := AccessLevel(doer, issue.Repo)
 	if issue.IsPull {
 		err = issue.PullRequest.LoadIssue()
 		if err != nil {