Code Quality: Tidy up notes-toggling code

[clinkingdog]

Notes-toggling code is just strings, not proper JavaScript. This makes it messy, harder to maintain, and notably hampers tool usage (which would, for example, have pointed out that about a 1/3 of the code there is currently unused).

Make the notes toggling script (notesToggleFunction) actual JS somehow: preferably a standalone file that's included somehow (sounds tricky with Windows security sadly), or alternatively a separate file of real JS that's then loaded and read as a string in the chrome extension, or at least some real JS where it currently is that then gets stringed (e.g. a function definition that you then call toString on).

Once that's changed, also tidy up the unused bits!