verify sender from VRS, not hardcoded client ID

[arcolife]

the client could just be anyone.
So verify the sender of the block by obtaining the VRS in block, deconstructing public key from that and comparing the obtained key with stored public key of the sender.

Also fix the 3 modes, 2 out of which are currently dummy, as per https://github.com/truechain/truechain-consensus-core/blob/master/README.md#step-3

4. `TRUE_SIMULATION` is as follows:
  - if set to 0 (default) - should tell the project to pickup testbed configurations. 
  - if set to 1 - staging, meaning all CI/CD tests are run before draft run. (dummy functionality at the moment)
  - if set to 2 - production. Will try to connect to boot nodes. (dummy functionality at the moment)

[samikshan]

I just want to document here what the function VerifySender currently does. func VerifySender(tx *pb.Transaction, n int) ([]byte, bool) currently verifies if a transaction has come from sender with index n, where 0 <= n <= N and the client is indexed as N for lack of addresses as of now. Inside the function we do recover the public key used to sign the transaction (the signature is in R || S || V format) and compare it with the public key of the sender indexed 'n'. If they match we infer that tx has indeed been sent by the sender with index n.

[arcolife]

+1

stuff for dev docs.