introduced BookElementsHolder class
Merge branch 'beta' into beta-ics
Merge branch 'master' into beta
Merge branch 'master' into ice-cream-sandwich
Merge branch 'ice-cream-sandwich' into beta-ics
synchronisation with intro branch
Merge branch 'master' into beta
Merge branch 'master' into ice-cream-sandwich
Merge branch 'beta' into beta-ics
Merge branch 'ice-cream-sandwich' into beta-ics