- 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

Make it easier to keep track of upstream changes and bug fixes

This adds a sqlite build tag so that you don't have to have the sqlite
import commented out in code and users can run:
    go build -tags sqlite
if they want to have sqlite support enabled.  It is disabled by default
so nothing changes with the default go get or build commands.