Repo management

[james-trayford]

Some changes to help manage the strauss repo better!

• add .gitignore file, mostly using GitHub boilerplate for python projects, but also adding WAV file ignores. This is a blanket ignore on all WAV files, with explicit exceptions for some of the data/samples packages bundled with strauss. if we add more bundles, will need to also append to .gitignore exceptions ('unignores')
• add a bin directory for helper scripts when working with strauss. first scripts set up the useful pre-commit hook for strauss developers that clears any output from ipython notebooks and re-adds them prior to commits, savig user from commiting (often large) output from .ipynb files
• add a "Github Action" that will explicitly check if any .ipynb files are still present in tests/pre-merge when trying to merge with main, and fail if so. This prevents merging into main with residual pre-merge tests present, to keep the main clean. Also add a readme.txt in this directory to explain this.

[james-trayford]

@SamYoules this should be ready for review now, added those pesky ipynb checkpoints to .gitignore, fixed the git hooks script and new pre-merge check - will just need to remove tests/pre-merge/dummy.ipynb when you're happy so the check doesn't trigger and we can merge!