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/timeline/index.go

@@ -81,7 +81,7 @@ grabloop:
 }
 
 func (t *timeline) IndexBehind(ctx context.Context, statusID string, include bool, amount int) error {
-	l := t.log.WithFields(logrus.Fields{
+	l := logrus.WithFields(logrus.Fields{
 		"func":    "IndexBehind",
 		"include": include,
 		"amount":  amount,