Add delta window function to postgres query builder

Explore: async starts of language provider

Org page to react

Increase Telegram captions length limit

Unlike the increase function delta doesn't check for resets
and can go negative. This is similar to the prometheus delta
function.

- 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