BDD: refactor Setup wizard

~~This is a simple refactor to use interfaces for sentences and the implementations on the contexts
( this is already done in every other bundle )~~

- [x] Move setup wizard sentences and implementations into an sub context

Also making minor changes regarding:
- [x] page identifiers (to lower cases)
- [x] change predefined $packages to be defined only on construct (to use same approach as the other variables)