Bug #691: Creation of multiple exhibits for one time
Issue686 Collection validation for Timelines, Exhibits & ContentItems

Issue868 Parent collection Validation
Merge branch 'master' of https://github.com/alterm4nn/ChronoZoom into Issue686ExhibitCollectionValidation
Bugfix for #643 - Initial timeline created with wrong data
Merge pull request #715 from alterm4nn/initialdatefix

Bugfix for #643 - Initial timeline created with wrong data
Merge pull request #712 from charuch/Issue686ExhibitCollectionValidation

Issue686 Collection validation for Timelines, Exhibits & ContentItems
Merge pull request #711 from javierluraschi/Fix691

Bug #691: Creation of multiple exhibits for one time
Convert the relative content item 'order' into absolute position within exhibit.