Train actinet using capture-24

[aidanacquah]

Implement functionality to make it possible to train an actinet classifier (both ssl and hmm) end-to-end.

This includes:

1. Download and preparation of capture 24 dataset
2. Adding fit functions to ActivityClassifier and sslmodel
3. Adding notebook outlining the end-to-end training and saving of the ActivityClassifier

This update also:

1. Reformats using Black formatter (for standardisation of code layout)
2. Minor update gitignore for new default save locations

[chanshing]

all looks good!
happy to merge!