React Gauge Panel - first step

Fix gofmt issues

See,
$ gometalinter --disable-all --enable=gofmt --deadline 10m --vendor ./...
build.go:1::warning: file is not gofmted with -s (gofmt)
scripts/build/release_publisher/externalrelease.go:1::warning: file is not gofmted with -s (gofmt)
scripts/build/release_publisher/localrelease.go:1::warning: file is not gofmted with -s (gofmt)
scripts/build/release_publisher/main.go:1::warning: file is not gofmted with -s (gofmt)
scripts/build/release_publisher/publisher_test.go:1::warning: file is not gofmted with -s (gofmt)

Remove Origin and Referer while proxying requests

[Bugfix] Don't drop the value when it's equal to None

Fix last megacheck issues

See, https://github.com/dominikh/go-tools/tree/master/cmd/megacheck

See,
$ gometalinter --vendor --deadline 6m --disable-all --enable=megacheck ./...
pkg/tsdb/influxdb/influxdb.go:106:3:warning: the surrounding loop is unconditionally terminated (SA4004) (megacheck)

See,
$ gometalinter --vendor --deadline 6m --disable-all --enable=megacheck ./...
scripts/build/release_publisher/publisher_test.go:14:2:warning: should merge variable declaration with assignment on next line (S1021) (megacheck)

Adjust UI depth of query statistics

Preserve suffix text when applying function suggestion

A z-index value of less than 1020 is needed because the time selection
dropdown shares the latter value via inheritance. Arbitrarily picked
1015 because it is a notch down.

Related: #14004

Updates all PromQL function-like suggestions to omit parentheses
when inserted. Such insertions also preserve any suffix text.

Related: #13885

[skip ci]

Adds more options for Slack notifications

Fix #13949
Fix #13328

Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>

Explore: Logging graph overview and view options

docs: restructure and enhancement