Ordering of variable observations is inconsistent

[daveey]

Describe the bug

When using a VECTOR observer, the observations are ordered by env.game.get_variable_names(). However, the same game yaml can result in a different order of variables on different machines. This makes it hard to re-use models.

To Reproduce Steps to reproduce the behavior:

I don't have a consistent repro, since it depends on the environment where griddly is built / running.

Expected behavior

I would expect game.get_object_names() and game.get_variable_names() to be consistent. They could either be ordered by when they appear in the yaml, or alphabetically by object_name.variable, followed by global variables

Desktop (please complete the following information):

• Version 1.7.0 (built from src)