Add subroutines to reset all user numbers for elements in a mesh

Tracker item: 2487
Merge branch 'master' of https://github.com/OpenCMISS/cm
Merge branch 'master' of https://github.com/xyan075/cm into xyan075-master
Merging pull request #183 plus fixes for the comments in the pull request
Bug fixes.
Merge pull request #189 from chrispbradley/master

Merging pull request #183