High: Shell: improve configure commit (lf#2336)

Implemented two different commit procedures:

• single element commit: this is the one which was already used; if the user's working on the live CIB, it is now used in concert with CIB shadows in order to prevent PE to kick in before all changes are committed
• whole-cib commit: the new one (cibadmin -R), used on big updates (more than 3 modifications or one quarter of all elements)

Mercurial revision: af20f826f79bf85ab2ec3525a09887c9d1fb528f