Web server - added charts, minor fixes

What's Changed

Web server

• Added a new battery chart
• Adding units to the config page
• Added icons to the dashboard page
• Remember the last tab selected (note this is global for now not per session)

• Web charts started work by @springfall2008 in #1419

Minor fixes

• Update "example_chart.yml" section "PV Forecast vs actual chart" by @stevensoave in #1410
• Minor documentation typos by @gcoan in #1421

New Contributors

• @stevensoave made their first contribution in #1410

Full Changelog: v8.4.4...v8.4.5