Additional possible cleanup in segmentations

[tmadlener]

Two comments that are not urgent (so merge if you want):

• Several member getters could return a const object (for example Phi() or phi() returning a double instead of a const double
• There are two members that could by statically allocated in GridDRcalo_k4geo.cpp, then the destructor doesn't need to be defined:

  k4geo/detectorSegmentations/src/GridDRcalo_k4geo.cpp

  Lines 26 to 27 in 550e75e

  	fParamBarrel = new DRparamBarrel_k4geo();
  	fParamEndcap = new DRparamEndcap_k4geo();

Originally posted by @jmcarcell in #517 (review)

[jmcarcell]

Actually const in the return type doesn't have any effects when returning by value. So the first comment doesn't apply to those functions.