Fixed bugs related to profile viewer and loading session files

[astrofrog]

This fixes several bugs:

• Fixed a bug with the profile viewer which caused layers to not update correctly when changing the reference data
• Fixed issue with reloading session with profile viewer that has a non-default reference data
• Improve how we deal with backward-compatibility related to change in Data.coords to None

[codecov]

Codecov Report

Merging #2078 into master will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2078      +/-   ##
==========================================
+ Coverage   90.22%   90.28%   +0.05%     
==========================================
  Files         397      397              
  Lines       39165    39245      +80     
==========================================
+ Hits        35338    35432      +94     
+ Misses       3827     3813      -14

Impacted Files	Coverage Δ
glue/viewers/profile/layer_artist.py	95.78% <ø> (ø)	⬆️
glue/core/tests/test_application_base.py	94.73% <ø> (-0.06%)	⬇️
glue/core/data_factories/helpers.py	91.93% <100%> (+0.22%)	⬆️
glue/viewers/profile/state.py	98.82% <100%> (+0.08%)	⬆️
glue/core/state.py	91.7% <100%> (+0.14%)	⬆️
glue/tests/test_session_back_compat.py	100% <100%> (ø)	⬆️
glue/viewers/profile/qt/tests/test_data_viewer.py	99.46% <100%> (+0.06%)	⬆️
glue/plugins/dendro_viewer/data_factory.py	100% <0%> (+2.27%)	⬆️
glue/app/qt/preferences.py	91.05% <0%> (+2.43%)	⬆️
glue/viewers/matplotlib/qt/widget.py	81.81% <0%> (+4.54%)	⬆️
... and 2 more

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