devenv: initial scripts for setting up devenv

[skip ci]

Fix CSS to hide grid controls in fullscreen/low-activity views

[skip ci]

fix singlestat threshold tooltip

Explore: Time selector, split view, design integration

* there was a comma missing to hide the handles, fixed now
* added new styles to hide header interaction in full screen panels

Fix cache busting for systemjs imports for plugins

[skip ci]

influxdb: support count distinct aggregation

this commit enable relatives path for provisioning dashboards.
this enables easier dev setups

Show create dashboard link if at least editor in one folder

Changed Prometheus interval-alignment to cover whole panel range

[skip ci]

As public/app/plugins/datasource/cloudwatch/partials/config.html and this file differ between the AWS regions available, I've updated the latest so they share the same data.
In that way, the regions() method in dashboards returns the same list as the frontend does.

graphite: avoid distributed tracing headers in direct/browser mode

Document table row merge for multiple queries

* everything imported via systemjs in the path `plugin/` will get a
 timestamp appended for cache busting
* timestamp is set once on page load
* plugin css loader gets cache buster too

docker: new block for elasticsearch6

[skip ci]

inviting users: show friendlier error message when smtp is not configured

Closes #12061