* extract actions on new pull request from models to pulls service
* improve code
* move code.gitea.io/gitea/modules/pull to code.gitea.io/gitea/services/pull
* fix fmt
* Rename pulls.go to pull.go
* refuse merge until ci successfully
* deny merge request when required status checkes not succeed on merge Post and API
* add database migration for added columns on protected_branch
* fix migration
* fix protected branch check bug
* fix protected branch settings
* remove duplicated code on check pull request's required commit statuses pass
* remove unused codes
* fix migration
* add newline for template file
* fix go mod
* rename function name and some other fixes
* fix template
* fix bug pull view
* remove go1.12 wrong dependencies
* add administrator bypass when protected branch status check enabled
* fix bug
* improve the codes
