Enable selection of multiple images

[blurry-mood]

Changes:

• select multiple images by default: index arg became indices
• by default no image is selected
• image_select return list of images instead of a single image, subsequently, the list is empty when no image is selected

TODO:

• [ ] update changelog in Readme.md

fixes #1

[jrieke]

Sorry, have seen this and your email but extremely oversubscribed with work right now. I'll make a task on my todo list to look through this once the most important projects have wrapped up but no guarantees!

[AyushExel]

hi @jrieke it'd be great if this feature is added to the original package. If not, could you please tell me how I can use this branch in my streamlit project? thanks!

[khronimo]

Hope this merge eventually gets looked at

[wjiang]

Hope that this pull request can be merged ASAP!