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 fd8249e99bcad0231e6ea65cd77c32aae9a54026.

* Fixing some auto refactor strangeness and typo.

* Making keys more human readable.

api4/system_test.go

@@ -7,7 +7,7 @@ import (
 	"strings"
 	"testing"
 
-	l4g "github.com/alecthomas/log4go"
+	"github.com/mattermost/mattermost-server/mlog"
 	"github.com/mattermost/mattermost-server/model"
 	"github.com/stretchr/testify/assert"
 )
@@ -392,7 +392,7 @@ func TestGetLogs(t *testing.T) {
 	Client := th.Client
 
 	for i := 0; i < 20; i++ {
-		l4g.Info(i)
+		mlog.Info(fmt.Sprint(i))
 	}
 
 	logs, resp := th.SystemAdminClient.GetLogs(0, 10)