Rename Icinga\Web\Form::onShow() to onRequest()

onShow() is misleading because at the time this method is being called the
form is neither shown nor created.

refs #5525
Fix spelling issue in german translation catalog
Add class ReadablePathValidator
Add the FormErrors decorator as default decorator for forms

This allows us to use Zend_Form::addError() to show error messages for
the entire form context.

refs #5525
Fix that the force_creation checkbox disappears after another error

Once the user enters invalid data after he tried to save a backend without
success (because the backend was not successfully validated) the shown
checkbox disappeared in this case regardless of whether it was checked
or not.

refs #5525
Rename ResourceForm and make it use handleRequest() & Co.

refs #5525
Remove BaseConfigController, User\Message and Widget\AlertMesageBox

refs #6758
ConfigController: Remove obsolete functionality
Remove remaining usages of the ElementWrapper- and HelpText-Decorator

refs #5525
lib: Use Zend's `Int' validator in the `Number' form element

Further disabled default decorators since our form sets them.

refs #5525
lib: Respect the disabled attribute in `FormNumber'

refs #5525
Replace usages of the `helptext' form element option with `description'

refs #5525
`FormNumber': Fix "The use statement with non-compound name..."

refs #5525
Merge branch 'bugfix/rebuild-form-builder-5525' into bugfix/commands-6593
lib: Let `DateTimeValidator' validate values as defined in HTML5

See http://www.w3.org/TR/html-markup/datatypes.html#common.data.datetime for the specification.

refs #6593
lib: Add function `isUnixTimestamp' to the `DateTimeFactory'

Before, the `DateTimeValidator' defined this function.

refs #6593
lib: Fix `DateFormat's `isUnixTimestamp' usage

refs #6593
lib: Add the HTML5 attributes 'min', 'max' and 'step' to the number input control

refs #6593
lib: Let the date-and-time input control behave as defined in HTML5

refs #6593
monitoring/commands: Fix `ToggleFeatureCommandForm::onSucces()'s PHPDoc

refs #6593