Add entity base class in Habitica integration

[tr4nt0r]

Proposed change

This introduces a base class for all entities to reduce code duplication:

• Refactoring of the sensor platform to be able to use base entity and reduce code duplication.
• Replaced previous method of recursively walking over the dictionary tree to access sensor values with a simple lambda function
• Moved DeviceInfo to the base class to reduce repetition of code
• Changed the task sensors to use the base class and added entity_description, which also reduces some duplicate code

Edit 1: Updated todos to also use the base entity class
Edit 2: Updated button platform to use the entity base class
Edit 3: Updated switch platform to use the entity base class

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:

Checklist

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[home-assistant]

Hey there @ASMfreaK, @leikoilja, mind taking a look at this pull request as it has been labeled with an integration (habitica) you are listed as a code owner for? Thanks!

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[home-assistant]

Please take a look at the requested changes, and use the Ready for review button when you are done, thanks 👍

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