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.

app/command_groupmsg.go

@@ -7,7 +7,7 @@ import (
 	"fmt"
 	"strings"
 
-	l4g "github.com/alecthomas/log4go"
+	"github.com/mattermost/mattermost-server/mlog"
 	"github.com/mattermost/mattermost-server/model"
 	goi18n "github.com/nicksnyder/go-i18n/i18n"
 )
@@ -95,7 +95,7 @@ func (me *groupmsgProvider) DoCommand(a *App, args *model.CommandArgs, message s
 
 	groupChannel, channelErr := a.CreateGroupChannel(targetUsersSlice, args.UserId)
 	if channelErr != nil {
-		l4g.Error(channelErr.Error())
+		mlog.Error(channelErr.Error())
 		return &model.CommandResponse{Text: args.T("api.command_groupmsg.group_fail.app_error"), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
 	}