XNAT-4400, XNAT-4434, XNAT-3978: Fixed and reconciled panel.select.menu and...

XNAT-4400, XNAT-4434, XNAT-3978: Fixed and reconciled panel.select.menu and select.menu widgets so they work consistently; added 'beforeElement' and 'afterElement' properties for Spawner elements - these will insert content before or after the MAIN element that's being spawned; added 'input.text.block' widget for inserting an <input> element with display: block style; added XNAT.spawner.resolve('elementNamespace/element') helper method for making requests to /xapi/spawner/resolve/elementNamespace/element; fixed (hopefully) styling of <iframe> elements in xmodal dialogs; explicitly set scope for JSP vars to help prevent multiple loads of certain .tag files.