Add scopes to the Guardfile

This prevents the integration tests from running when changes to model classes are made and vice versa.

Guard can also be started in a specific scope with 'guard -g unit'
Improve expressiveness: Use 'x.next' instead of 'x += 1'
Fix regex to match ids higher than 9
Update TODOs
Prevent unit tests from using the hooks in $HOME.

Before, for instance, TestBreak instantiated a plain Break, which will happily call the real ~/.paradeiser/hooks/*, which is surely not what we want.
Update test script that creates failing hooks in HOME