+ added global variable unitContextIndex (index of the current info in the...

+ added global variable unitContextIndex (index of the current info in the unit's context array) to contextTabController to be able to distinguish between add and edit mode
# replaced contextDataCounter and contextDataIndex with this variable
# replaced id in array_multiSelectionContextInfos with this index
# distinguished adding of icons to unit: when editing context, the icon gets replaced, otherwise a new one is added
TODO: select2 doesn't seem to work correctly anymore on new array_mutli...