add annotation buttons

[tamidodo]

Closes #26

Adds buttons for freeform open/closed, circle, rectangle and "stop drawing" which switches it back to "pan" mode.

[github-actions]

Staging application has been deployed and is available at: https://dash5-services.plotly.host/ml-exchange-staging
Production app name: ml-exchange
Current branch name: custom-annotation-buttons
Commit: fb4d2ad

[hannahker]

Love it! Everything works well on my testing. Just have some UI change requests:

• Can we make each button the same size and just display the icon, with the text in a tooltip? We should then be able to fit all 5 across in the same row, which would match vertically with the annotation classes below.
• Can we have some visual indication for which button is currently selected? Maybe the background is coloured a slightly darker shade.
• Let's have the "open freeform" option selected by default when the page loads.

[hannahker]

Perfect, LGTM 💃