CRM-15490 - Recurring entity QA fixes

https://issues.civicrm.org/jira/browse/CRM-15256 :   
Points 1 & 2 is fixed. Point 3 is something not supported by recurring entity. Datetime column if used with propagation algorithm, would just copy over the same dates.
However there is a workaround, we can modify recurring configuration, which should re-generate the set considering the new datetime.
Agree that propagation confirmation box just for date/time updates could be misleading. We could probably notify this to user some way?

https://issues.civicrm.org/jira/browse/CRM-15490 :  
1, 3, improvements are done. Also added some webtests (4).