Add configuration api

[andig]

Refs #6029

• add /config/templates/<class> api
• prepare templates for json export
• some internal renames
• add config/test/<class> api
• simple config form for vehicles with testing ability @naltatis

For testing:

curl -X POST --data '{"template":"dsmr","host":"foo"}' http://localhost:7070/api/config/test/meter
{"error":"cannot create meter 'template': cannot create meter 'dsmr': dial tcp: lookup foo: no such host"}

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new vehicle creation dialog (WIP)

enable "Experimentals" (only in dev & nightly) to reveal the "Add vehicle" option

[andig]

make toml