mapType attribute superfluous

[MarAlder]

Both the stringVectorBaseType and arrayVectorBaseType have the attribute mapType (="vector" and ="array") which is required.

Since the data type is fixed by the schema (users may look into the documentation and this tutorial on how to read the documentation) the mapType attribute is not necessary.

Furthermore, the mapType frequently leads to confusion because users interpret it as switch between a double and vector/array type. However, XSD 1.0 unfortunately does not support this.

Therefore, the mapType attribute should be set optionally. In this way old data sets are still valid. In a next major release the attribute should be removed.

Also refer to DLR-SC/tixi#143.