Block::createDataArray: Add data_type + shape args

Adjust all tests for that change.
DataArray: remove createData methods

They are no longer needed.
DataArray: remove hasData() method

Is now always true because Block::createDataArray does
create the underlying DataSet.
Merge pull request #299 from gicmo/createDataArray

Block::createDataArray: Add data_type and shape args

LGTM