Issue due date api (#3890)

* Implemented basic api endpoint to manage deadlines

* Fixed checking for permissions

* Updating a deadline from the ui is now entirely done via the api

* cleanup

* Cosmetics

* fixed lint + fmt

* Added swagger model definition for deadline response

* Updated gitea-sdk

* Updated gitea-sdk

* More cleanup

* Generate swagger json

* Merge branch 'master' of https://github.com/go-gitea/gitea into issue-due-date-api

# Conflicts:
#	public/swagger.v1.json

* Fixed permission to update a deadline via api

* Re-added form to change a deadline

* Added client-side validation + not ignore error messages from the api

* Added locale for error message

* Merge branch 'master' of https://github.com/go-gitea/gitea

# Conflicts:
#	models/issue_comment.go

* Proper date validation

* Fixed indention

* moved css to css file

* added documentation for error codes

* after merge cleanup

* Added swagger description

* DO NOTHING BUT TRIGGER THAT F*CKIN CI SO IT PICKS UP THE LATEST COMMIT AS IT SHOULD

* DO NOTHING BUT TRIGGER THAT F*CKIN CI SO IT PICKS UP THE LATEST COMMIT AS IT SHOULD

* regenerated stylesheets

routers/api/v1/api.go

@@ -447,6 +447,8 @@ func RegisterRoutes(m *macaron.Macaron) {
 							m.Combo("").Get(repo.ListTrackedTimes).
 								Post(reqToken(), bind(api.AddTimeOption{}), repo.AddTime)
 						})
+
+						m.Combo("/deadline").Post(reqToken(), bind(api.EditDeadlineOption{}), repo.UpdateIssueDeadline)
 					})
 				}, mustEnableIssues)
 				m.Group("/labels", func() {