Refactor serialization and deserialization

[shomykohai]

Summary

This PR aims to refactor the Serialization/Deserialization process.

• Updated how serialize_quests() works -> Now the serialization process is done by the Quest itself, the manager just calls it and retrieve the serialized data. It's suggested to override this method for better control over the process.
• Added deserialize_quests to the quest manager ->As for serialize_quests, it calls a method on the quest.
• Added get_all_pools() to the quest manager.
• Added get_pool to the quest manager.
• Added get_all_quests() to BaseQuestPool

Documentation

• Updated documentation to reflect the changes listed above
• Added more documentation inside of the addon itself.

Closes #20

Checklist

• This PR changes something in the code (e.g. for better performance).
  • If any code changes had taken place, I've tested them before committing.
  • I've properly updated the documentation to reflect the changes I've made.
• This PR adds something new.
• This PR fixes an issue.
• This PR includes breaking changes.
• This PR is not code related (e.g. README, Documentation)

[shomykohai]

This does not change quests_as_dict and dict_to_quests method name as planned in #20 as it could lead to breaking changes.
The methods name will be changed in future versions.