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