Fixing issue with validation in checkable file

Validation state doesn’t matter if the element is checkable and not
checked.
Setting the size policy for container instances

Helps the Container classes to only take up as much space as needed.
This is especially relevant when expanding/collapsing containers.
Adding a debug print function

Will add more to this function later on.
Fixing a container collapsing issue

toolkit-level collapsible containers containing elements were not being
disabled because a NotYetImplemented error was encountered.
Disabling contained elements when collapsed
Converting "tabbedGroup" -> "tabGroup"

Close issue #10
Dropdown.current_index() is now type-aware

Updates #11
Dropdown.current_index() is now type-aware

Updates #11