Create base class for Environment

[alvarofpp]

Following the package standard for DRL, we need the class to have the following methods:

• start: Starts the environment.
• step: Executes an action in the environment, and returns a tuple of [Observation, Reward, Done].
• reset: Resets the environment and returns an Observation.
• close: Closes the environment.

Suggestions:

• Class name: EnvironmentBase.
• Class path: urnai.environments.
• Source: https://github.com/UFRN-URNAI/urnai-tools/blob/main/urnai/envs/base/abenv.py .

Notes:

• This is an abstract class, so it is important that it inherits from abc.ABC.
• You don't need the Savable class.