Added support for 15 minute price resolution (#1031)

* 15min prices WIP

* WIP more changes for 15min prices

* More work on 15min pricing

* Fixed some errors

* Some changes after testing

* Graphical changes for 15min pricing

* Adjustments on MQTT handlers after switching to 15min prices

* Reverted some MQTT changes

* Adapted HA integration for 15min pricing

* Adapted JSON payload for 15min

* Adjustments during testing

* Set default price interval

* Fixed refresh of price graph when data changes

* Bugfixes

* Fixed some issues with raw payload

* Adjustments for meter timestamp from Kamstrup

* Updated readme

* Added detailed breakdown of payloads coming from Norwegian meters

* Minor changes relating to price

* Fixed byte alignment on price config

* Changes to support RC upgraders

lib/SvelteUi/json/conf_price.json

@@ -2,5 +2,6 @@
     "e": %s,
     "t": "%s",
     "r": "%s",
-    "c": "%s"
+    "c": "%s",
+    "m": %d
 },