Fixes #11758

Explore: add support for multiple queries

* docs: further documents changes to the docker image.
* docs: explains the changes to user id better.

* notification-service-refactor2:
  fix: removed log calls used while troubleshooting
  refactor: refactoring notification service to use new service registry hooks

Explore UI skeleton

* adds +/- buttons to query rows in the Explore section
* on Run Query all query expressions are submitted
* `generateQueryKey` and `ensureQueries` are helpers to ensure each
 query field has a unique key for react.

* refator: refactored PluginManager to be a self registering service, a lot more work needed to fully make plugin manager use instance variables and not so many globals

revert renaming of unit key ppm

* extensions: import and build

* bus: use predefined error

* enterprise: build script for enterprise packages

* poc: auto registering services and dependency injection

(cherry picked from commit b5b1ef875f905473af41e49f8071cb9028edc845)

* poc: backend services registry progress

(cherry picked from commit 97be69725881241bfbf1e7adf0e66801d6b0af3d)

* poc: minor update

(cherry picked from commit 03d7a6888b81403f458b94305792e075568f0794)

* ioc: introduce manuel ioc

* enterprise: adds setting for enterprise

* build: test and build specific ee commit

* cleanup: test testing code

* removes example hello service

#11211 removed the unit key ppm in favor of conppm. A change which is not forward compatible.
This commit revert the unit key back to ppm.
Also adds some better error description if trying to use a unit which don't exists.
Fixes #11743

* mjtrangoni-fix-deadcode-issues:
  tech: removes unused code
  add deadcode linter to circleci
  pkg: fix deadcode issues
  build.go: fix deadcode issues

Merge branch 'fix-deadcode-issues' of https://github.com/mjtrangoni/grafana into mjtrangoni-fix-deadcode-issues

* 'fix-deadcode-issues' of https://github.com/mjtrangoni/grafana:
  add deadcode linter to circleci
  pkg: fix deadcode issues
  build.go: fix deadcode issues

fix so that google analytics script are cached

prometheus: variable query should fallback correctly to a series query 

sql tsdb: fix value columns conversion to float when using timeseries query

fix misalignment of unit and other drop downs in firefox

removed height 100% from panel-container to fix ie11 panel edit mode

Add weback-dev-server with hot/hmr support

Using a query of for example up or up{job=job1}