Update CHANGELOG.md

Minor grammar tweaks and formatting.

fix sql query in GetAdminStats.

fixes #3879

Send OpenTSDB POST request as urlencoded

Update CHANGELOG.md

Fixed dashboard_tag query

Triggers grafana packer CircleCI build after successful build of master branch

Only triggers for main grafana repo (not forks) and when the
master branch is built.

Grafana stats view as mentioned in #3812

fix(graph): narrow panels shows correct date format on x-axis

fixes #3852. The function that calculates the date format for
the x-axis on a panel takes the panel width into account and
can be wrong for certain date ranges if the panel is too
narrow. E.g. can show dates in format %m/%d %H:%M when it
should show it as %H:%M

Serialize an elasticsearch error previously printed as 'Object'

Fixed broken tags search

Updates documentation for SingleStat thresholds

The implementation of thresholds changed after fixing #3248. Docs
updated to reflect and explain the change.

npm for node 4 on circleci is really old. This updates npm and will
hopefully make the build green again.

If OpenTSDB is 3rd-party hosted (or by another team) and does not support OPTIONS, send the request as POST (urlencoded)