Semantic segmentation module becomes sluggish with several regions annotated

[royschwartz2]

Describe the bug
When annotating several regions and labels the program becomes very sluggish. For example, zooming in and out takes a long time, hiding/unhiding annotations takes time.

To Reproduce
Steps to reproduce the behavior:
Annotate several regions and labels (seems like it's more of a problem with different labels)

Expected behavior
According to the release notes this problem was fixed with version 1.1.

Screenshots
If applicable, add screenshots to help explain your problem.

Environment (please complete the following information):

• OS: MacOS 11
• Label Studio Version 1.1

Additional context
Add any other context about the problem here.

[nick-skriabin]

please, take a look at LS 1.2, it contains some performance optimizations regarding image segmentation

[makseq]

Hope this fixed. Feel free to re-open