Fix all the resting errors to have a valid swagger file.

They are still some warnings but nothing blocking.

Doing so I found that some request still misses son parameters for some POST/PUT/PATCH request. This means the a client generated from the swagger file will not work completely. 

Fix #4088 by activating validation in drone
Should fix #4010.

* Replace all ctx.Handle with ctx.ServerError or ctx.NotFound

* Change Handle(403) to NotFound, avoid using macaron's NotFound

* refactor struct's time to remove unnecessary memory usage

* use AsTimePtr simple code

* fix tests

* fix time compare

* fix template on gpg

* use AddDuration instead of Add

* Update swagger documentation

Add docs for missing endpoints
Add documentation for request parameters
Make parameter naming consistent
Fix response documentation

* Restore delete comments

From code.gitea.io/go-sdk/gitea
  To code.gitea.io/sdk/gitea

- Update import paths from github.com/go-gitea to code.gitea.io
- Fix import path for travis

See https://docs.travis-ci.com/user/languages/go#Go-Import-Path