Store IDs of DataArrays using section name and Name attribute

Summary

This MR changes the way IDs are created to identify DataArray Attributes, PointsData and CellData. The ID is composed of section name and DataArray name. This allows to have DataArray elements in multiple sections with the same Name.

Example

A DataArray with Name="MyField" in the section PointData is stored by the ID

id="PointData.MyField"

Exceptions

The DataArray in the Points section does not necessarily have a Name attribute and if it has one, the name is irrelevant. There must be exactly one DataArray element in the Points section. So, the ID is explicitly fixed to Points.