added possibility to set format of videoPlayer

is necessary because if width and height of video is 100% means responsive,
the width and height of previewImage has to be calculated with contentWidth and format
set 16:9 format as default value for VideoPlayer
videoPlayer is now more flexible for set user defined width or an responsive width

in form will be used cards now to select contentWidth or userDefinedWidth,
for the first you can choose than an format (16:9, 4:3) and for the second you can set a specific pixel value
added trl for videoPlayer
Merge pull request #125 from kaufmo/3.5_imageDimensionsResponsiveVideoPlayer

Add possibility to set format of videoPlayer