DataSet::dataType: support the compound type for nix::Value

This should close issue #296
[test] DataSet: add check for correct dataType of Value dataset
DataSet::read(Value): dataType supports Value now, use it
Merge pull request #297 from gicmo/issue_296

DataSet::dataType: implement support for Value's compound type
create Property creates a dataset instead of a group, Added Dataset to Property contructors
enabled attributes in DataSet. Copy-paste from Group. Should be extracted...
skip validation in TestProperty, Section creates a dummy dataset ...
create Property creates a dataset instead of a group, Added Dataset to Property contructors
skip validation in TestProperty, Section creates a dummy dataset ...
unit attribute working
createProperty needs a Value. new method with vector of Values
changes in Property::values method to use the dataset instead the group
add a dummy value for creating properties
style fixes, Property::mapping set updated only in case a change was done
fixed failing Section::hasProperty method
fixed Property::values(vector<Value>)
fixed Property::dataType
fixed ProptertyHDF5::valueCount
fixed bug in SectionHDF::createProperty with single values
add dummy values for testProperty