Add support for seperate meters

internal/migrations/files/0004.sql

@@ -0,0 +1,10 @@
+CREATE TABLE meter (
+	id           serial       PRIMARY KEY  NOT NULL,
+	name         varchar(255)              NOT NULL,
+	fortop_uid   varchar(50)               NOT NULL
+);
+
+DELETE FROM measurement;
+
+ALTER TABLE measurement
+	ADD meter_id integer                   NOT NULL;