Improve usability of viewpage module with:

* Added a default option with width and height set to auto
* Selection is saved in $GLOBALS['BE_USER']->uc using ExtDirect
StateProvider and restored after reload or page switch
* Frame is resizeable and this custom value is also stored in the user
settings as a new option of the selector
* iframe is visually separated from outer module body

Change-Id: I0f956b3b3b76ef5fea25c239acd8f95d4f93b765
Fixes: #51933
Releases: 6.2
Reviewed-on: https://review.typo3.org/23771
Tested-by: Philipp Gampe
Reviewed-by: Mattias Nilsson
Tested-by: Mattias Nilsson
Tested-by: Markus Klein
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer