Improve accuracy of Predbat savings calculation

What's Changed

• The Predbat savings calculation needs to use a starting SOC value, this is now tracked based on the previous days simulation rather than assumed based on the actual behaviour which would be Predbat led.

• Make sure IBoost and Car charging modeling is disabled during savings calculation.

---

• Fixes to try to make savings correct by @springfall2008 in #1105
• Fix SOC tracking for savings by @springfall2008 in #1108

Full Changelog: v7.19.0...v7.19.1