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/pull.go

@@ -458,7 +458,7 @@ func (pr *PullRequest) Merge(doer *User, baseGitRepo *git.Repository, mergeStyle
 		return nil
 	}
 
-	mode, _ := AccessLevel(doer.ID, pr.Issue.Repo)
+	mode, _ := AccessLevel(doer, pr.Issue.Repo)
 	if err = PrepareWebhooks(pr.Issue.Repo, HookEventPullRequest, &api.PullRequestPayload{
 		Action:      api.HookIssueClosed,
 		Index:       pr.Index,
@@ -787,7 +787,7 @@ func NewPullRequest(repo *Repository, pull *Issue, labelIDs []int64, uuids []str
 
 	pr.Issue = pull
 	pull.PullRequest = pr
-	mode, _ := AccessLevel(pull.Poster.ID, repo)
+	mode, _ := AccessLevel(pull.Poster, repo)
 	if err = PrepareWebhooks(repo, HookEventPullRequest, &api.PullRequestPayload{
 		Action:      api.HookIssueOpened,
 		Index:       pull.Index,