add histogram, scatter, and volume viewers to registry

[kecnry]

This PR adds missing viewers (histogram, profile, volume, and image) to the viewer registry.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (0976a06) 86.62% compared to head (bb511ad) 86.65%.
Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #402      +/-   ##
==========================================
+ Coverage   86.62%   86.65%   +0.02%     
==========================================
  Files          89       89              
  Lines        5130     5154      +24     
==========================================
+ Hits         4444     4466      +22     
- Misses        686      688       +2     

Files	Coverage Δ
glue_jupyter/bqplot/histogram/viewer.py	100.00% <100.00%> (ø)
glue_jupyter/bqplot/image/viewer.py	87.67% <100.00%> (+0.17%)	⬆️
glue_jupyter/bqplot/profile/viewer.py	97.91% <100.00%> (+0.09%)	⬆️
glue_jupyter/ipyvolume/volume/viewer.py	100.00% <100.00%> (ø)

... and 5 files with indirect coverage changes

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[astrofrog]

@kecnry - could you also add the image viewer?

[kecnry]

@astrofrog - not sure how I missed that one! Added.