Links any AbstractComponent to an Upload component. This means that upon a click on the linked component this click will be "forwarded" to the uploader and trigger its file selector window. Multiple uploaders can be successively linked to a single upload; multiple components can also be linked to a single uploader. Simply call link(AbstractComponent, Upload) for each component/uploader combination. Known limitations: * The linking is not permanent. If you reload a page you must reapply it. * Both the component and the uploader *must* be added towards the view where you want to use them. * Both the component and the uploader *must* be visible (i.e., don't use Component#setVisible(boolean) with *false* as this removes the component from the DOM. * After the linking the upload component will be made invisible via CSS (style.display='none'). This may affect your layout! So best add the uploader at a convenient space - for instance at the bottom * The component and the uploader *must* have their IDs set. See: Upload#setId(String), AbstractComponent#setId(String) * These IDs *must* be unique. * In case you build your UI lazily ensure that the components you want to link are present. This method waits an increasing amount of time (25ms, 50ms, 75ms, ...) * for the components to be found and will time out after about 12s (30 attempts). (You can check successful/failed linkings via your browser's console.) * Other registered ClickListeners will still fire for the source and target component.