Enable error and no_data overrides when testing alerting.

* fix(alerting): fixed evaluation for no_value condition, fixes #7244

* feat(alerting): moving null library into grafana, fixing handling on no value / no series

closes #7149

With present postinst script on Centos 7, restart after upgrade is not working with Warning: grafana-server.service changed on disk. Run 'systemctl daemon-reload' to reload units.

So i added systemctl daemon-reload.

Fix typo in tags API documentation example request

ref #7234

* add s3 dependencly

* rewrite image uploader by aws-sdk-go

* improve backward compatibility of s3 image uploading

* set default for expires option

* remove acl and expires

change(text panel): removed rarely used (and not properly working), text mode option, closes #6389, closes #7214

feat(templating): completed work on built in template variables  and , closes #7190, refactors #7170

Fix webhook username mismatch

Fixing variable name mismatch so that the Authorization HTTP header is added to webhook notifications.