Fix #2003: Have a way of seeing what session file was opened

[specmicp]

This commit add the session filename in the window title

The window title is updated on export, restore and reset.

[codecov]

Codecov Report

Merging #2096 into master will decrease coverage by 0.01%.
The diff coverage is 93.82%.

@@            Coverage Diff             @@
##           master    #2096      +/-   ##
==========================================
- Coverage   87.98%   87.97%   -0.02%     
==========================================
  Files         245      244       -1     
  Lines       22132    22279     +147     
==========================================
+ Hits        19473    19600     +127     
- Misses       2659     2679      +20     

Impacted Files	Coverage Δ
glue/viewers/image/state.py	91.31% <ø> (ø)
glue/viewers/profile/state.py	98.83% <ø> (+0.01%)	⬆️
glue/viewers/image/layer_artist.py	89.62% <60.00%> (+0.14%)	⬆️
glue/core/data_combo_helper.py	91.53% <77.77%> (-0.45%)	⬇️
glue/app/qt/application.py	78.63% <90.90%> (+0.13%)	⬆️
glue/core/data_factories/pandas.py	85.00% <100.00%> (ø)
glue/core/qt/layer_artist_model.py	83.69% <100.00%> (ø)
glue/viewers/common/viewer.py	90.59% <100.00%> (ø)
glue/viewers/scatter/layer_artist.py	97.83% <100.00%> (-0.29%)	⬇️
glue/viewers/scatter/qt/layer_style_editor.py	93.86% <100.00%> (+0.76%)	⬆️
... and 16 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 39eaaf0...026f50f. Read the comment docs.

[astrofrog]

Looks great, thanks! I just pushed a small tweak to make sure it works fine when loading session files from the command-line.