[skip ci]

WIP: Fit panels to screen height

Explore: show message if queries did not return data

- every result viewer displays a message that it received an empty data
  set

- position was determined by SPACE, but Prometheus selectors can
  contain spaces
- added negative lookahead to check if space is outside a selector
- moved braces plugin into PromQueryField since braces are prom specific

Explore: Add history to query fields

* build: makes the grafana docker image smaller.

* build: branches and PR:s builds the docker image.

Mssql: add logo

unix socket docs

- _.reverse() was modifying state.history

- queries are saved to localstorage history array
- one history per datasource type (plugin ID)
- 100 items kept with timestamps
- history suggestions can be pulled up with Ctrl-SPACE

Merges the Grafana docker build into the main repository.

* Explore: facetting for label completion

- unified metric and non-metric label completion
- label keys and values are now fetched fresh for each valid selector
- complete selector means only values are suggested that are supported
  by the selector
- properly implemented metric lookup for selectors (until the first
  metric was used which breaks when multiple metrics are present)
- typeahead tests now need a valid selection to demark the cursor

* Fix facetting queries for empty selector

Karma to Jest: variable_srv

Karma to Jest: OpenTSDB datasource