Make reload/restart easier by identifying changed configuration items

[mdeweerd]

The list of YAML configurations that can be reloaded on '/config/server_control' is pretty long.

It's also not always clear if the change that was just applied needs a restart or could just be done with a partial reload.

Sometimes I try a partial reload, then test, observe that there was no change and reload.
So the time of reloading and testing the first time are then lost time.

I think that is is possible to improve this expérience for the user:

• Changes can be detected by comparing the "on disk" configuration with the "in memory" configuration.
• Home Assistant can classify the changes in the appropriate categories: input, scene, template, etc.
• The categories that changes could be highlighted in some way, including the restart button.
• A button "Reload all changed configurations" could be added.
• The configuration page could inform about why a restart is needed.
• A state could be added to detect that a restart is needed, that the configuration is valid, and possibly a state for each category requiring a restart (that could allow automating the restart process).
• When reading the configuration, the list of files involved could be memorized, changed to these files could be notified by the system (iwatch on *nix, other method on Windows). This can trigger a read of the new configuration.
• Advanced: Configuration history could be kept in the database and changes could be made examinable using the UI. Complete internal representations of the configuration be kept. (A configuration change could be detected by comparing a checksum of the json representation for instance).