Bug fixes for clipping & pause mode, unit testing

What's Changed

Bug fixes

Fixed a number of bugs, including modelling of clipping & pause mode when car is charging.

• Potential fix for spurious charges by @springfall2008 in #1236
• Adding unit tests, fixed bug in AC Coupled mode with clipping by @springfall2008 in #1240
• Prediction unit testing, inverter clipping bug by @springfall2008 in #1242
• Further unit tests, fix for discharge freeze by @springfall2008 in #1243
• Set charge rate to full during discharge by @springfall2008 in #1244
• Leave pause mode enable when car charges by @springfall2008 in #1246

Unit testing

Added initial set of unit tests for the simulation model. Instructions on how to run in the developer docs area.

• Adding unit test to file list by @springfall2008 in #1245

Full Changelog: v8.1.0...v8.1.1