Avoid redirecting internal rendering requests

closes #11180

[ci skip]

dashboard: fix import dashboard with alert rule(s)

middleware: recover and retry on session start

Importing a dashboard with alert rule(s) should be possible without receiving invalid
alert data error. This fix reverts the import logic to how it worked before Grafana v5.0,
that is import will allow dashboard with alert rule(s) but no alerts will be created.
After an import the user will need to update the dashboard for the alerts to be created.
Fixes #11227

Should be possible to browse dashboard using only uid

alerting: supports extracting alerts from collapsed panels

Partial fix for #11155 - the Macaron session middleware
panics if mysql returns an error. This fix recovers from
the panic and retries once

collapsed rows wrap the hidden rows within itself. This caused
the extractor to miss the panel and therefore delete the alert
accosiated with the graph.

closes #11222

Added icon for iOS web app

That is, the slug part of url should be optional.

That is, the slug part of url should be optional.
Closes #11231

If you using Safari on a iOS device and save the page to home screen you will get the Grafana icon as icon

Got added by mistake a year ago.

[ci skip]

Add color to prefix and postfix in singlestat panel

[ci skip]

* Seconds to HH:MM:SS format

[ci skip]

Prometheus heatmap support

Added concentration units and "Normal cubic metre"

docs: fix an outdated link to Prometheus's doc

ppm, ppb, ng/m3, ng/Nm3, μg/m3, μg/Nm3, mg/m3, mg/Nm3, g/m3, g/Nm3, Nm3
ppm was moved from "Dimensionless" and "submenu" to "Concentration"

Fix urls in plugin update_checker logs