Clarify some variable names and save by file stem as default

[paddyroddy]

Fixes #243

[deprecated-napari-hub-preview-bot[bot]]

Preview page for your plugin is ready here: https://preview.napari-hub.org/quantumjot/btrack/391 Updated: 2023-08-09T16:31:20.170496

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (a9609bc) 85.74% compared to head (b4f1be7) 85.74%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #391 +/- ## ======================================= Coverage 85.74% 85.74% ======================================= Files 31 31 Lines 2202 2203 +1 Branches 404 404 ======================================= + Hits 1888 1889 +1 Misses 232 232 Partials 82 82 ``` | [Files Changed](https://app.codecov.io/gh/quantumjot/btrack/pull/391?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Alan+R+Lowe) | Coverage Δ | | |---|---|---| | [btrack/napari/main.py](https://app.codecov.io/gh/quantumjot/btrack/pull/391?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Alan+R+Lowe#diff-YnRyYWNrL25hcGFyaS9tYWluLnB5) | `65.69% <100.00%> (+0.25%)` | :arrow_up: | | [btrack/napari/widgets/\_general.py](https://app.codecov.io/gh/quantumjot/btrack/pull/391?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Alan+R+Lowe#diff-YnRyYWNrL25hcGFyaS93aWRnZXRzL19nZW5lcmFsLnB5) | `100.00% <100.00%> (ø)` | |

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[paddyroddy]

I think the name changes are good and it makes sense to set the name based on the filename. It would be great if here:

https://github.com/quantumjot/btrack/blob/b4cad6aa00016df441d56dc8b3daffd88516abf8/btrack/napari/main.py#L375

you check if the config name already exists and if so either:

* automatically change the config name (e.g. append a `1` or `a`)

* ask the user if they want to overwrite the existing config or cancel

Have tried and failed to do the latter. My plan was that it would exit and tell the user that they need to adjust the filename. See my attempt #392, but I don't have time to continue this. Can you please unblock me?