Tutorial doc fix

[Chilipp]

• Closes A couple usability notes #3 (remove if there is no corresponding issue, which should only be the case for minor changes)

[Chilipp]

This PR is ready to be merged. It improves the docs on the selection toolbar and the interactive navigation in the user guide and the tutorial. In particular:

• it adds docs on the pixel row and pixel column selection tool (see the tutorial and user guide)
• it adds a note that the navigation has to be disabled when moving marks (see the tutorial on navigation and on selecting the data part)

It will be merged if @ixjlyons approves the changes.

[codecov]

Codecov Report

Merging #5 into master will decrease coverage by 2.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master       #5      +/-   ##
==========================================
- Coverage   88.17%   86.11%   -2.07%     
==========================================
  Files          26       26              
  Lines       11313    11247      -66     
==========================================
- Hits         9975     9685     -290     
- Misses       1338     1562     +224

Impacted Files	Coverage Δ
straditize/common.py	44.44% <0%> (-55.56%)	⬇️
straditize/colnames.py	47.94% <0%> (-43.39%)	⬇️
straditize/widgets/colnames.py	65.82% <0%> (-22.34%)	⬇️
straditize/magnifier.py	91.66% <0%> (-1.41%)	⬇️
straditize/binary.py	87.91% <0%> (-0.13%)	⬇️
straditize/widgets/tutorial/beginner.py	94.05% <0%> (-0.04%)	⬇️
straditize/widgets/menu_actions.py	74.56% <0%> (+0.1%)	⬆️
straditize/straditizer.py	89.8% <0%> (+0.79%)	⬆️
straditize/__main__.py	82.79% <0%> (+2.79%)	⬆️

---

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[codecov]

Codecov Report

Merging #5 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master       #5   +/-   ##
=======================================
  Coverage   88.17%   88.17%           
=======================================
  Files          26       26           
  Lines       11313    11313           
=======================================
  Hits         9975     9975           
  Misses       1338     1338

---

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 9fc92ce...a86ce67. Read the comment docs.