[Settings] Adds an active flag to the settings fieldset.

* Users can now choose, wether they want to override the defaults (from the config array) or not.
* The javascript hides the customize element, if the activate checkbox is not checked.

(refs #5455, gh-50)
[Applications] ApplyController considers isActive-flag of form settings containers.

(refs #5455, gh-50)
Merge branch 'feature/fix_form_element_settings' into develop