Fixed  #109 (Update Change number of drops in Identity class) and #128 (Fixed Identity constructor should set QblPrimaryKeyPair)

Update Change number of drops in Identity class #109 
Fixed  Identity constructor should set QblPrimaryKeyPair #128

Please also check the issue #147 because a test crashed
I'd think that having a List won't force the API user to cast the collection back into the List if he/she wants to change its contents.
If the drops-List shall be read-only or immutable, we'd have to change the interface even further, probably.