Improve Transaction Handling: WaitForTransactionReceipt, Signing, & Keystore

[PsychoPunkSage]

Following improvements were raised by @thiagodeev

1. The WaitForTransactionReceipt wasn't working as intended in the examples. Is there any potential issue in the method?

2. The SignInvokeTransaction, SignDeployAccountTransaction, and SignDeclareTransaction should receive a Broadcast<type>Transaction instead of a <type>transaction since is the Broadcast tx that will be sent with the AddTransaction methods. We can also think about having an account.SignTransaction method that under the root calls dynamically one of these methods...

3. We can think about having an account.AddTransaction method that under the root calls dynamically one of Add<type>Transaction methods.

4. The MemKeystore needs both public and private keys as parameters to be initialized, but sometimes it is a bit difficult to find the public key. Why not just require the private key from the user and use some methods available by the curve package to dynamically derive the public key?