Move darkstorm_backend to just backend

Added MongoDB instances of DB tables
Updated some DB interfaces
Added logging to count cleanup

internal/backend/key.go

@@ -0,0 +1,12 @@
+package backend
+
+type ApiKey struct {
+	Perm  map[string]bool
+	ID    string
+	AppID string
+	Death int64
+}
+
+func (k ApiKey) GetID() string {
+	return k.ID
+}