Maximize/Stretch logic now works in stage
xml tag added to remember the screenMode setting
test to check remembering of screen mode
new function getScreenMode()
and used the enum to get the strings
fixed test
needs longer sleep time, otherwise a NullPointerException happens
added errormasseges to tescase
refectoring
fix saveScreenshot after Maximize/Stretch
"Streched" is now the standart view in the stage.
Merge pull request #730 from Catrobat/MaximizeStretch

save ScreenMode in XmlHeader