Wow! Thanks a lot!!
I would like to suggest using a StackedLayout(/Widget) for the actual data,
you can see an example here.

So when the program starts up you get the category list, you select a category and then you go 'down' the stack into the entries list, and when you select that you go 'down' the stack to the actual info.

This will also allow splitting up the menus between each stack to have only the relevant entires. (For example, creating a new group, only in the group list, creating a new entry only in the entry list, copying the password only the info page, etc...)

Thanks again for your work!