Explore: still show rate hint if query is complex

Explore: Filter out existing labels in label suggestions

Explore: Fix initial state in split view

- if the suggestions menu is open, apply the selected item on Enter
- if not open, run the queries

dsproxy: interpolate route url

* Remove unrequired extract-text-webpack-plugin

* Update ngAnnotate to avoid deprecation warning

* Avoid deprecation warning (Tapable.plugin -> hooks)

Allows for dynamic urls for plugin routes. There are a few plugins
where the route url should be configurable and this change allows
using jsonData fields in the url field for a route in the
plugin.json file for a plugin.

Related to #12944

[skip ci]

Provisioning: Should allow one default datasource per organisation

Login button issue in light theme

[skip ci]

add $__unixEpochGroup and $__unixEpochGroupAlias to sql datasources

Doc - fix broken link

removed inverse btn styling and added bgColor to generic oauth and grafana.com login buttons, added styling so log in button uses dark theme inverse btn styling both for dark and light theme

There's no per-row contextual menu anymore
Instead there's a  option

Closes #12862

Closes #10784

Set User-Agent header in datasource proxied requests

Header value will be Grafana/%version%, i.e. Grafana/5.3.0

Fix typo

Fixes #12524

[skip ci]

GitLab authentication backend