Code improvements and bug fixes.

Notable changes

Danish translation added @dykandDK.
Code improvements and simplifications for data observers handling.
API throttling to make sure APIs are not called more often than allowed.

Changes

Bug Fixes

• Fix for price/kWh sensor not updating on all chargers on a site. @olalid (#578)
• Cost refresh updated to comply with 10 calls per hour limit @olalid (#569)

Translation

• Lokalise: Translations update @astrandb (#585)
• Lokalise: Translations update @astrandb (#583)

Code quality and maintenance

• Simplify observers handling in ProductData @olalid (#570)
• Cost refresh updated to comply with 10 calls per hour limit @olalid (#569)