Proof-of-concept: Masks

We are really excited to share some work-in-progress about masking. This will be really powerful: you can mask a group of animated layers with any animated mask. We have a working prototype of this, and we can't wait to share it publicly with you!

Other improvements and fixes

• Improved the behavior of clicks on the timeline
• Animations now keep the same order in the timeline when grouping / ungrouping them
• Layers now keep the same order in the timeline when grouping / ungrouping them
• Fixed a bug that would cause a conflict between a Move and other overlapping animations