Remove property aliases for StartTime and EndTime

[axunonb]

@minichma t.b.d.:
Unify property names using Start and End? or StartTime and EndTime?
Remove aliases DtStart, DtEnd

Reasoning: Simply the public API

[axunonb]

@minichma What do you think? Leave as is?

[minichma]

Some consolidation would certainly be good, I don't think it's a top prio though. Given the limited resources, I think it would be ok to leave it for V6.