Move towards selectable time ranges in the dashboard

- Add the installation date to frontend and backend
- Add an error page to help with the upgrade from the previous version
- Avoid querying history if installation date is not set
- Make the fillMissing function work for periods of different lenght than than 8 days

README.md

@@ -52,6 +52,7 @@ As soon as you navigate to the container's exposed port, you will see the admin
 
 - **HomeAssistant's base URL**: the base URL which you use to access HomeAssistant on your server. It should be something like `http://INTERNAL_IP_ADDRESS:8123/` or `https://homeassistant.youdomain.com/`.
 - **HomeAssistant's API Key:** Get it by going into your HomeAssistant profile settings (at `http://HOMEASSISTANT-BASE-URL/profile`) -> Create Long Lived Access Token (at the very bottom of the page) -> Insert a name -> Copy the string it gives you
+- **Installation Date**: Select the date of the first day in which your server's consumption was logged in its entirety. Users won't be able to see consumption data before this date.
 - **Polled Smart Energy Summation entity ID:** After your plug is added in HomeAssistant, get it in Overview -> look for an entity called like "[Name of your plug] Polledsmartenergysummation" -> Settings -> Copy the Entity ID. Check that the unit of measurement in the "Info" tab is kWh.
 - **CO2 signal Grid fossil fuel percentage entity ID**: Get it in Settings -> Devices and Integrations -> Add Integration -> CO2 Signal -> Get your token from the website -> CO2 signal Grid fossil fuel percentage -> Settings -> Copy the Entity ID. Check that the unit of measurement in the "Info" tab is %.
 - **Admin username and password** don't need to be the credentials to HomeAssistant! They are the credentials to log into the admin panel.