Refs #4394 moved initialization steps from constructor to init
Refs #4394 Moved ElasticDiffSphere inside of DiffSphere
Refs #4394 Moved some initialization steps to init

These changes for the elastic part
Refs #4394 Moved inelastic part under DiffSphere files
Refs #4394 Some refactoring
Refs #4394 redoing the unit test
Refs #4394 Explicit check of boundaries
Refs #4394 correct silly format syntax
Refs #4394 Wrote four unit tests
Refs #4394 add numeric header
Refs #4394 Reduced random variability in initial guess
Refs #4394 Added WIKI header
Refs #4394 Reduced random variability in initial guess

The initial guess can be too far from the optimal parameters so that
the fitting procedure is unable to converge
Refs #4394 Return infinity for negative parameters

Change return zero for return infinity. Garanteed a bad chi-square
Refs #4394 More details for the WIKI page
Merge remote-tracking branch 'origin/feature/4394_diffusion_sphere'