Fix infinite toggle loop

[nmearl]

Resolves #185. Fixes an issue when manipulating the data collection that could result in an infinite loop occurring with the toggled data list items.

🚨NOTE FOR FUTURE REFERENCE🚨 Please, do not attempt to alter application state from within plugins! This can have obviously unintended consequences due to event ordering!

[rosteen]

It doesn't look like moving the code in now in the app._on_data_deleted method out of the plugin solves the loop issue, I was still able to replicate the infinite loop behavior after deleting the relevant code from the model fitting plugin. Tested from a clean install.

EDIT: wow, I meant does not solve the loop issue, the original comment was thus rather confusing.

[nmearl]

@rosteen, locally, does this solve the looping issue seen in #185 with the unit conversion plugin?

[rosteen]

No, I'm still able to replicate the looping with the unit conversion as well.

[nmearl]

I cannot replicate with this PR -- are you testing with the Specviz Unit Conversion notebook?

[rosteen]

I was using the Specviz hack hour notebook. I had to change units 6 or 7 times before the flickering/looping started, but through persistence was able to break it.

[javerbukh]

Could not replicate bug in a clean conda environment even after about 10 tries (I am using Chrome for my browser, if that helps).

[rosteen]

Forgot to actually approve - I am still seeing odd behavior very occasionally, but I think at this point the root cause is my browser/local notebook behaving poorly rather than a code fix needed.