Transaction issues for alert reminder

Explore: jump to explore from panels with mixed datasources

use alert state changes counter for alert notification dedupping.

Fix megacheck issues

typo in sample.ini

Update to ldap.md

See,
pkg/tsdb/cloudwatch/credentials.go:45:2:warning: should merge variable declaration with assignment on next line (S1021) (megacheck)

See,
pkg/cmd/grafana-server/main.go:107:8:warning: '_ = <-ch' can be simplified to '<-ch' (S1005) (megacheck)

See,
pkg/tsdb/stackdriver/stackdriver_test.go:356:2:warning: 'if err != nil { return data, err }; return data, nil' can be simplified to 'return data, err'

I removed some code, and commented out other one.

See,
$ gometalinter --vendor --disable-all --disable=gotype --enable=megacheck --deadline 6m ./... | grep unused
pkg/api/avatar/avatar.go:100:26:warning: func (*CacheServer).mustInt is unused (U1000) (megacheck)
pkg/api/folder_test.go:136:6:warning: func callGetFolderByUID is unused (U1000) (megacheck)
pkg/api/folder_test.go:141:6:warning: func callDeleteFolder is unused (U1000) (megacheck)
pkg/api/live/hub.go:40:15:warning: func (*hub).removeConnection is unused (U1000) (megacheck)
pkg/components/imguploader/azureblobuploader.go:130:5:warning: var client is unused (U1000) (megacheck)
pkg/middleware/middleware_test.go:438:28:warning: func (*scenarioContext).withInvalidApiKey is unused (U1000) (megacheck)
pkg/services/alerting/ticker.go:40:18:warning: func (*Ticker).updateOffset is unused (U1000) (megacheck)
pkg/services/notifications/notifications_test.go:12:6:warning: type testTriggeredAlert is unused (U1000) (megacheck)
pkg/services/sqlstore/dashboard_service_integration_test.go:935:6:warning: type scenarioContext is unused (U1000) (megacheck)
pkg/services/sqlstore/dashboard_service_integration_test.go:939:6:warning: type scenarioFunc is unused (U1000) (megacheck)
pkg/services/sqlstore/dashboard_service_integration_test.go:941:6:warning: func dashboardGuardianScenario is unused (U1000) (megacheck)
pkg/services/sqlstore/transactions_test.go:13:6:warning: type testQuery is unused (U1000) (megacheck)

cli: fix reset-admin-password 

- extends handlers for panel menu and keypress 'x'
- in a mixed-datasource panel finds first datasource that supports
  explore and collects its targets
- passes those targets to the found datasource to be serialized for
  explore state
- removed `supportMetrics` and `supportsExplore`
- use datasource metadata instead (set in plugin.json)
- Use angular timeout to wrap url change for explore jump
- Extract getExploreUrl into core/utils/explore

Explore: Store UI state in URL

13411 react api key

If notification state is pending and last update of state was made
less than a minute ago. In the case of a grafana instance is shut down/crashes
between setting pending state and before sending the notification/marks as complete
this logic should allow the notification to be sent after some time instead of
being left in an inconsistent state where no notifications are being sent.

Stackdriver Datasource - Fixes #6733