Backend image rendering as plugin (#11966)

* rendering: headless chrome progress

* renderer: minor change

* grpc: version hell

* updated grpc libs

* wip: minor progess

* rendering: new image rendering plugin is starting to work

* feat: now phantomjs works as well and updated alerting to use new rendering service

* refactor: renamed renderer package and service to rendering to make renderer name less confusing (rendering is internal service that handles the renderer plugin now)

* rendering: now render key is passed and render auth is working in plugin mode

* removed unneeded lines from gitignore

* rendering: now plugin mode supports waiting for all panels to complete rendering

* fix: LastSeenAt fix for render calls, was not set which causes a lot of updates to Last Seen at during rendering, this should fix sqlite db locked issues in seen in previous releases

* change: changed render tz url parameter to use proper timezone name as chrome does not handle UTC offset TZ values

* fix: another update to tz param generation

* renderer: added http mode to renderer service, new ini setting [rendering] server_url

Gopkg.toml

@@ -100,13 +100,17 @@ ignored = [
   version = "1.1.1"
 
 [[constraint]]
-  branch = "master"
-  name = "github.com/grafana/grafana_plugin_model"
+  branch = "renderer"
+  name = "github.com/grafana/grafana-plugin-model"
 
 [[constraint]]
   branch = "master"
   name = "github.com/hashicorp/go-hclog"
 
+[[constraint]]
+  name = "github.com/hashicorp/go-plugin"
+  revision = "e8d22c780116115ae5624720c9af0c97afe4f551"
+
 [[constraint]]
   branch = "master"
   name = "github.com/hashicorp/go-version"