allow to set "current" codepage on createWBXML
allow to set "current" codepage on createWBXML

So far a call to tbSync.wbxmltools.createWBXML("") created an empty
wbxml element, which was at codepage 0 (AirSync). If we want to use
append more often, so that wbxml createion can be splitted into
functions, it needs to know its current codepage (Calender, Tasks etc.)

jobisoft/TbSync,jobisoft/TbSync,jobisoft/TbSync