Don't sync color and transparency of image layers by default

[astrofrog]

@nmearl - this should prevent the sync issues you were seeing

[nmearl]

👍 Awesome! Thanks.

[codecov]

Codecov Report

Merging #2116 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2116   +/-   ##
=======================================
  Coverage   87.98%   87.98%           
=======================================
  Files         244      244           
  Lines       22270    22279    +9     
=======================================
+ Hits        19595    19603    +8     
- Misses       2675     2676    +1     

Impacted Files	Coverage Δ
glue/viewers/image/state.py	91.01% <100.00%> (-0.30%)	⬇️
glue/viewers/profile/layer_artist.py	95.74% <0.00%> (-0.05%)	⬇️
glue/app/qt/application.py	78.63% <0.00%> (+0.13%)	⬆️
glue/__init__.py	70.37% <0.00%> (+3.70%)	⬆️

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