* 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
* move all mail related codes from models to modules/mailer
* fix lint
* use DBContext instead Engine
* use WithContext not WithEngine
* Use DBContext instead of Engine
* don't use defer when sess.Close()
* move DBContext to context.go and add some methods
* move mailer from modules/ to services
* fix lint
* fix tests
* fix fmt
* add gitea copyright
* fix tests
* don't expose db functions
* make code clear
* add DefaultDBContext
* fix build
* fix bug
* move create release from models to a standalone package
* fix lint
* fix comment year
* fix lint
* fix lint
* fix package import name
* fix vendor
* fix go mod
* some refactors
* fix vendor
* use go1.12 make vendor
* fix vendor
Elias Norberg
Lunny Xiao
Daniel Fonseca de Lira