ImageFolder add option to ignore some folders like '.ipynb_checkpoints'
Maybe it would be nice to ignore private dirs like this one (ones starting with `.`) by default. 

CC @mariosasko 
**Is your feature request related to a problem? Please describe.**
I sometimes like to peek at the dataset images from jupyterlab. thus '.ipynb_checkpoints' folder appears where my dataset is and (just realized) leads to accidental duplicate image additions. I think this is an easy enough thing to miss especially if the dataset is very large.

**Describe the solution you'd like**
maybe have an option `ignore` or something .gitignore style
`dataset = load_dataset("imagefolder", data_dir="./data/original", ignore="regex?")`

**Describe alternatives you've considered**
Could filter out manually

