QoL improvements and more docs

[bengioe]

This PR is (unfortunately) fairly massive, but is mostly renaming things, or removing things that aren't needed anymore.

• Updated README.md
  • Added docs/contributing.md and docs/getting_started.md
  • Added (a link to) an introductory notebook, runnable on colab
• Renamed FlatRewards into ObjectProperties, as well as related function names
• Renamed RewardScalar into either LogScalar or LinScalar, as well as changed the function signature of functions accordingly
• Removed all passing around of rng instances, replaced by get_worker_rng to remove any confusion around worker seeding
  • Similarly, dev should now be acquired via get_worker_device
• None-proofed cond_info in models. There should now be a sensible default behavior. Eventually we should properly make sure the code support unconditional tasks
• Made cfg.git_hash computational conditional on being in a git repo
• Renamed generic functions and methods working with objects to obj[s] rather than mol[s]
• Made terminate close log files (to avoid issues when a single process runs multiple trials)
• Added a read_all_results function in sqlite_log.py. This is probably the fastest way to load log data
• Fixed a number of mypy issues.

[julienroyd]

LGTM!