Optimized calculation of available energy for car charging

What's Changed

• Updated service to show an average available power graph in the UI by @tocosonic in #8
• Optimized power calculation by @tocosonic in #9
• Support minimal charger-only setup by @tocosonic in #7
• using moving average car charging power and non-used energy buffer by @tocosonic in #10

Full Changelog: 1.3.3...1.4.0