Fix to incremental rates, improvement to charge curve calcs

What's Changed

• Rate scaling divide by 0 protection in charge curve calcuation by @springfall2008 in #681
• Automatic unit detected for Watts vs Kwh when reading historical data by @springfall2008 in #682
• Charge curve averaging and auto mode by @springfall2008 in #683
• Fix to repeat of incremental rate adjustments by @springfall2008 in #685

Full Changelog: v7.15.9...v7.15.10