add retrieveFeatureData for Tags to util::dataAccess
add retrieveFeatureData for MultiTags in util::dataAccess
add test for feature data access
etended test to check for data access of tags that point to slices
TestDataAccess: initials for feature data for multiTags
add retrieveFeatureData method to MultiTag
add retrieveFeatureData method to Tag
rename of method parameter for consistency
minor spelling corrections in exception texts
bugfixes in dataAccess.retrieveFeatureData
finished test for retrieveFeatureData for MultiTags
fix of uninitialized stack allocation
Merge pull request #392 from jgrewe/feature_data

Feature Implemented methods to retrieve data of features

LGTM