Issue due date (#3794)

* Started adding deadline to ui

* Implemented basic issue due date managing

* Improved UI for due date managing

* Added at least write access to the repo in order to modify issue due dates

* Ui improvements

* Added issue comments creation when adding/modifying/removing a due date

* Show due date in issue list

* Added api support for issue due dates

* Fixed lint suggestions

* Added deadline to sdk

* Updated css

* Added support for adding/modifiying deadlines for pull requests via api

* Fixed comments not created when updating or removing a deadline

* update sdk (will do properly once go-gitea/go-sdk#103 is merged)

* enhanced updateIssueDeadline

* Removed unnessecary Issue.DeadlineString

* UI improvements

* Small improvments to comment creation
+ ui & validation improvements

* Check if an issue is overdue is now a seperate function

* Updated go-sdk with govendor as it was merged

* Simplified isOverdue method

* removed unessecary deadline to 0 set

* Update swagger definitions

* Added missing return

* Added an explanary comment

* Improved updateIssueDeadline method so it'll only update `deadline_unix`

* Small changes and improvements
* no need to explicitly load the issue when updating a deadline, just use whats already there
* small optimisations

* Added check if a deadline was modified before updating it

* Moved comment creating logic into its own function

* Code cleanup for creating deadline comment

* locale improvement

* When modifying a deadline, the old deadline is saved with the comment

* small improvments to xorm session handling when updating an issue deadline
+ style nitpicks

* style nitpicks

* Moved checking for if the user has write acces to middleware

templates/repo/issue/list.tmpl

@@ -216,6 +216,10 @@
 								<span class="octicon octicon-milestone"></span> {{.Milestone.Name}}
 							</a>
 						{{end}}
+						{{if ne .DeadlineUnix 0}}
+							<span class="octicon octicon-calendar"></span>
+							<span{{if .IsOverdue}} class="overdue"{{end}}>{{.DeadlineUnix.FormatShort}}</span>
+						{{end}}
 						{{if .Assignee}}
 							<a class="ui right assignee poping up" href="{{.Assignee.HomeLink}}" data-content="{{.Assignee.Name}}" data-variation="inverted" data-position="left center">
 								<img class="ui avatar image" src="{{.Assignee.RelAvatarLink}}">