Allow typing text in "Model" combo box

[Enyium]

There are other compatible models available than the ones in the fixed list. In #69, I added one. Others include the ...distil... models from here. Since you already have the ....en models in the list, adding the ...distil... models may be warranted. In any case, it would be useful to input your own Hugging Face "username/repository" identifiers into the combo box. And since Qt combo boxes can be made editable, this shouldn't be a problem.

However, there can be problems with crashes when using incompatible models. It would need to be ensured that the user can change it again using the GUI instead of being locked out by crashes on app start-up.