Add napari-btrack-reader to this package

[dstansby]

This adds the napari reader as an optional napari plugin to this package. This is entireley optional, and I've configured most of the tests to check that the btrack can still be run fine without napari installed. To check that the optional napari bits work there is now an extra tox environment that runs the tests with napari installed. I've also added some docs on how users can install the dependencies needed for the napari plugin.

I anticipate we will add btrack-napari in a similar way in a separate PR in the future.

Fixes https://github.com/lowe-lab-ucl/napari-btrack/issues/7
Fixes lowe-lab-ucl/napari-btrack-reader#3

[codecov-commenter]

Codecov Report

Merging #115 (842c9a0) into main (443f984) will decrease coverage by 0.08%.
The diff coverage is 76.66%.

@@            Coverage Diff             @@
##             main     #115      +/-   ##
==========================================
- Coverage   80.79%   80.71%   -0.09%     
==========================================
  Files          13       14       +1     
  Lines        1432     1462      +30     
==========================================
+ Hits         1157     1180      +23     
- Misses        275      282       +7     

Impacted Files	Coverage Δ
btrack/napari/reader.py	76.66% <76.66%> (ø)

---

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 443f984...842c9a0. Read the comment docs.

[dstansby]

@quantumjot could you install the napari-hub preview app on this repository, so we can get the preview comments: https://github.com/apps/napari-hub ?

[quantumjot]

could you install the napari-hub preview app on this repository

Should be done now.

[deprecated-napari-hub-preview-bot]

Preview page for your plugin is ready here:
https://preview.napari-hub.org/quantumjot/BayesianTracker/115
Updated: 2022-05-25T11:57:47.278623

[alessandrofelder]

Looks largely good!
Some very minor points that I think were there before this PR in the other repo.
Variable names could be improved a bit, I think? (but as part of a separate PR)

[paddyroddy]

Nothing critical but some suggestions which should improve the code quality

[paddyroddy]

I have addressed the comments in the PR since I've reviewed so going to merge