adds a test that verify that null values are not used
when calculating the median value in alerting

closes #10056

alerting: increase default duration for queries

Add [hash] to grafana.{light,dark}.css

we should promote using longer queries since this should
increase the quality of the alerts. only using a 5min range
means that we will only have 4 datapoints in data is written
every min which is not good enough for the generic alert rule

Fix minor JSON typo in HTTP API docs

Updated login page logo & wordmark and responsive behavior

[skip ci]

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