update ImmuClientverifiedGet to return VerifiableEntry instead ofEntry

[artiomi]

Hello
Current implementation of rpc VerifiableGet returns instance of type VerifiableEntry. At same time ImmuClient.verifiedGet return instance of type Entry.
Considering fact that that VerifiableEntry is a more complex class than Entry, ex: it contains more details about transaction in VerifiableTx, I have added new classes VerifiableEntry, VerifiableTx which now match rpc call response and update ImmuClient.verifiedGet to return VerifiableEntry instance.
In order to avoid impact on existing library users, VerifiableEntry extends Entry class.

Artiom

[vchaindz]

Awesome, this addresses everything cleanly.

Thanks for signing the commits too.