Available sizes in viewpage module can be configured with Page
TSConfig mod.web_view.previewFrameWidths. Defining a height
property is optional.

Change-Id: I7900959bc76fc2c586307c0fd4200f9665876dd3
Resolves: #51865
Documentation: #52783
Releases: 6.2
Reviewed-on: https://review.typo3.org/23720
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters