add header tag to code.xml

to get a header tag in our code.xml
(containing all project related information except
spritelist) a 'dummy' headerclass is needed to store
all headervalues
forgot XmlHeader class...
set setter and getter package private
fix testVersionName
Language version update to 0.5
Merge pull request #193 from Catrobat/xmlHeaderTag

add header tag to code.xml