[RpcNep5Tracker] Using contract id instead of contract scriptHash.

[nicolegys]

Now the plugin uses contract scriptHash to creat a key in storage.

Shall we use contract id instead? Since now we support migrating/destroying a contract, the scriptHash could be changed/deleted.
Maybe we also need to handle notifications other than transfer, to handle the migration/destroy scenes.

[shargon]

Yes, we should do it

[ProDog]

This can be reopened? the scriptHash could not be changed if contract migrated. @Tommo-L

[Tommo-L]

Yes, plz reopen it.