Add support for groups in the widget dropdown

a.dmitriiev → made their first commit to this issue’s fork.

I have added the property category to the plugin attribute and also the options in third party settings now have the categories as groups. If no category is set, the plugin will be under "Other" option group. Please review.

Nice work. I've added the category to the ECA field widgets and the result is exactly as expected. Thanks you so much.