Add config entry for custom VAT

[catshapednoodles]

Added a config entry to overwrite the hardcoded VAT values. As discussed in #163, this would be a better solution than just temporarily changing the value. This way all users have a way to easily change VAT values if their situation calls for that, without changing the code.

Also added UI translations for other languages than English, but I don't know if they are any good since I got them from Google Translate.

[Hellowlol]

Thanks for the PR. As I mentioned in the issue. I want to use the template for this.

https://github.com/custom-components/nordpool/blob/master/custom_components/nordpool/sensor.py#L268-L270
I pretty use we can just add the current_hours_price async_render function :)

[Hellowlol]

Closing this in favor of #165 as i dont want to add more config options and adding price to the template allows more flexibility .

Thanks for the PR