Add checks to ensure robustness DICOM Attributes defined in multiple Modules

[tomaroberts]

Realised that some DICOM Attributes are defined in more than one Module, e.g.:

• BitsAllocated is defined in both Image Pixel Module and MR Image Module

Current behaviour means that which ever Module is called second overrides. Not ideal.

TODO:

• when calling Module subclasses, check if Attributes already exist in the Dicom object and then perform relevant logic, e.g. overwrite and warn.