improve lightbox sizing with forms

callOnContentReady before measuring size of lightbox as forms use
ResponsiveEl and change their height
don't return height if adaptHeight is not set and maxSize is not reached

fixes size adapdation of forms with height below window height
callOnContentReady when hiding errorEl

fixes size adapdation of lightbox forms
ResponsiveEl: re-evaluate every time callOnContentReady is called

callOnContentReady is also called if content is shown/hidden or changes it's size (lightbox)
we have to re-evaluate in those cases.
callOnContentReady after sizing and positioning lightbox to support responsive form in lightbox
ResponsiveEl: callOnContentReady when changing class

required for responsive form in lightbox
avoid flicker in ie8 where there is no proper domready event

this allows ResponsiveEl to add class before any content is displayed
HelpText for VideoPlayer Upload
Translation for HelpText in VideoPlayer