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

templates/repo/issue/view_title.tmpl

@@ -6,7 +6,7 @@
 				<input value="{{.Issue.Title}}">
 			</div>
 		</h1>
-		{{if .IsIssueOwner}}
+		{{if or .IsIssueWriter .IsIssuePoster}}
 			<div class="four wide column">
 				<div class="edit-zone text right">
 					<div id="edit-title" class="ui basic green not-in-edit button">{{.i18n.Tr "repo.issues.edit"}}</div>