Explore: async starts of language provider

Org page to react

Increase Telegram captions length limit

- changed `start()` to return promise on main language feature task
- promise resolves to list of secondary tasks
- speeds up time to interaction of metric selector
- lazy loading of certain metric selector and log label selector items
- loading indication of metric and log label selectors

IE11 fix for legend tables below graph

Add only display date option to table panel column

[skip ci]

[skip ci]

mysql graphical query builder

Explore: repair logging after recent Explore restructuring

this is a fix-up PR that cleans up Explore Logging after the recent
restructuring.

- log results need to be merged since query transactions have been
  introduced
- logging DS has its own language provider, query field, and start page
  (some of them based on prometheus components)
- added loader animation to log viewer
- removed logging logic from prometheus components

Explore: Pluggable components from datasource plugins

JS tooling: run TS grunt tasks only when files changed

* Add new build info metrics that contains more info

The goal was to add more information about Grafana. But rather than
just adding those to the current metrics I created a new metric
since its a common pattern in the prometheus community to expose that
info in a metric named `*_build_info`.

We keep the old metric to avoid introducing any breaking changes but
we should be able to remove it the next breaking change