Alert tab ux update

Fixed timepicker css issue introduced by PR #14700 and remove hotfix …

14719/gauge issues

Fixed new gotmetalinter warning

Don't cut off subsecond precision for postgres macros

Change time format to RFC3339Nano for $__timeFilter, $__timeFrom and
$__timeTo macros

Explore: Remember last used datasource

Fixed issues with panel size in edit mode, fixes #14703

Update yarn.lock

Loki: query limit configurable in datasource

Logs data model: add more log levels

Tweak datetime picker layout for mobile

- use local storage to store last used database
- renamed `datasourceName` property to `initialDatasourceId` for consistency
- adapted tests

only update session in mysql database when required

fix only create/drop database indices if not exists/exists

- add `eror` used in github.com/inconshreveable/log15 (used by Grafana as well)
- add levels from SYSLOG

Loki: change query row to be single field again

Explore: logging UI style fixes

Explore: fix loading indicator z-index on panel container

- existing z-index placed the loading indicator above dropdowns of the panel children
- removed z-index for natural ordering

- tried split selector and search for a week, and it did not feel natural
- keeping some of the original modifications in QueryField from splitting PR
- adapted CheatSheet and placeholder text
- added new label selector state: No labels found