Consistent storage and access schema for bounds

VolumeBounds and SurfaceBounds have currently:

• different storage schemas (which will make it difficult to serialise)
• different naming conventions for parameters
• different access methods

This is resolved by introducing a common way to store the initial parameters in an internal array/vector and by creating a single access schema for this.

Additional measure:

• it will harmonise the naming of bounds variables
• it should also remove TDD_real_t as this needs too be consistently done