Structured logging (#8673)

* Implementing structured logging

* Changes to en.json to allow refactor to run.

* Fixing global logger

* Structured logger initalization.

* Add caller.

* Do some log redirection.

* Auto refactor

* Cleaning up l4g reference and removing dependancy.

* Removing junk.

* Copyright headers.

* Fixing tests

* Revert "Changes to en.json to allow refactor to run."

This reverts commit fd8249e99b.

* Fixing some auto refactor strangeness and typo.

* Making keys more human readable.

store/sqlstore/preference_store.go

@@ -6,9 +6,9 @@ package sqlstore
 import (
 	"net/http"
 
-	l4g "github.com/alecthomas/log4go"
 	"github.com/mattermost/gorp"
 
+	"github.com/mattermost/mattermost-server/mlog"
 	"github.com/mattermost/mattermost-server/model"
 	"github.com/mattermost/mattermost-server/store"
 )
@@ -38,7 +38,7 @@ func (s SqlPreferenceStore) CreateIndexesIfNotExists() {
 }
 
 func (s SqlPreferenceStore) DeleteUnusedFeatures() {
-	l4g.Debug("Deleting any unused pre-release features")
+	mlog.Debug("Deleting any unused pre-release features")
 
 	sql := `DELETE
 		FROM Preferences