Improve development time application reload

[fjvallarino]

This PR implements several improvements to the development workflow:

• Reuse the active window when saving changes to files and reloading the application. This handles the feature requested here: Ghcid not working properly #88
• Reuse the latest version of the model when saving changes and reloading the application. This allows for a faster development experience since the application will be restored to its previous state (in most cases, at least)

To take advantage of the model reuse feature, applications need to provide a new configuration attribute. If the model implements a derived version of Show, it can be enabled as follows:

config = [
...
  appModelFingerprint show
...
]

The appModelFingerprint function receives a function from the model's type to String. Details can be found here.

[Dretch]

I just had a play around with this. It mostly worked nicely: it is good to be able to keep the same window and model 😄

One issue I had is that I had to save a file twice before the UI updated: the first time I saved the file, ghci printed *** Exception: <<loop>> - but then when I re-saved it worked as expected. I was using a .ghcid file like this one: https://github.com/fjvallarino/monomer-starter/blob/main/.ghcid (only difference is the app name) and no .ghci file, on Linux (the project is private but I can probably make a project to demo the issue).

[fjvallarino]

@Dretch wow, I missed this too 😞. I was reviewing this PR in order to merge it and saw the comment.

I wonder if it's related to not having the .ghci file. I'll test more tomorrow to see if I can replicate it.

Thanks for testing it!