Fix open containers simplification

[MarcCote]

This pull request introduces several updates to the ScienceWorld project, including documentation improvements, new developer instructions, adjustments to simplification presets, and minor codebase enhancements. The most important changes are grouped below by theme.

Documentation Enhancements:

• Added a new "Simplifications" section in README.md, explaining the available simplifications and the --simplifications-preset argument, including a warning about differences from the paper's description.
• Introduced a "Developers" section in README.md with detailed instructions for building the ScienceWorld JAR file, including prerequisites and steps for installation and compilation.

Simplification Preset Updates:

• Updated the help text for the --simplifications-preset argument in examples/human.py and examples/random_agent.py to specify the exact simplifications applied by the easy preset. [1] [2]

Developer Tooling:

• Added a new dev extras group in setup.py to include development dependencies from requirements-dev.txt.

Codebase Maintenance:

• Updated the version in simulator/build.sbt from 1.2.2 to 1.2.3 to reflect the new changes.
• Refactored the SimplificationOpenContainers logic in SimplifierProcessor.scala to use a more generic EnvObject type instead of Portal for handling container objects.

[MarcCote]

Fixes #76

[PeterAJansen]

Looks good!