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

- using grunt-newer to prefix precommit tasks
- only got it to work for tslint and tsc

Not applied to:

- sasslint does not take the file arguments in a way that grunt-newer
  recognizes
- no-only-tests throws an error when used with `newer`, but it's
  sub-second runtime