reference global logrus (#274)

* reference logrus' global logger instead of passing and storing a logger reference everywhere

* always directly use global logrus logger instead of referencing an instance

* test suites should also directly use the global logrus logger

* rename gin logging function to clarify that it's middleware

* correct comments which erroneously referenced removed logger parameter

* setting log level for tests now uses logrus' exported type instead of the string value, to guarantee error isn't possible

internal/processing/streaming/openstream.go

@@ -31,7 +31,7 @@ import (
 )
 
 func (p *processor) OpenStreamForAccount(ctx context.Context, account *gtsmodel.Account, streamType string) (*stream.Stream, gtserror.WithCode) {
-	l := p.log.WithFields(logrus.Fields{
+	l := logrus.WithFields(logrus.Fields{
 		"func":       "OpenStreamForAccount",
 		"account":    account.ID,
 		"streamType": streamType,