Make sub release date optional to inherit end date Merged

Master Releases push their dates onto sub releases - this should be optional - it would be better in some cases to see the grey bar for a sub release be shorter because it is confusing when all sub releases have the same date as master. 

Also it would better if it were possible to have dependency dots after the grey bar of the release because otherwise we have to make a milestone called "launch" or something that reprepsents when the release finishes - there doesn't seem to be a way to link releases (the end date) to say a phase in the master release, etc., would sometimes is the product planning requirement.