Optimize history_stats efficiency and database usage

[bokub]

Description:

Change various things on the history_stats component, mostly for optimization:

• Don't compute a new value if the period hasn't changed and the current time is not in the period (issue History Statistics Sensor is permanently consuming high amounts of CPU load #7800)
• Remove the from and to attributes. Because they change constantly, they currently write a new state in database at every update, which is really not good. They are useless
• Don't display seconds in the value attribute

Related issues:-

• partially fixes History Statistics Sensor is permanently consuming high amounts of CPU load #7800
• Attributes named 'to' are hidden in the /states interface #7270 doesn't make sense anymore

Pull request in home-assistant.github.io with documentation: home-assistant/home-assistant.io#2733

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• Tests have been added to verify that the new code works.

[balloob]

Thanks 🐬