initials for retrieve data
new checker: is position in the data extent
test for position checking methods
implementation of retrieve data for DataTags

Conflicts:
	include/nix/util/dataAccess.hpp

Conflicts:
	src/util/dataAccess.cpp
test for retrieve data for DataTags
add retrieveData for SimpleTag
Test for retrieving data from SimpleTag
removed tautological warning
Merge pull request #223 from jgrewe/retrieve_data

Retrieve referenced data from DataTag and SimpleTag 

LGTM