Facilitator: Unlock worker address.

[deepesh-kn]

This is an implementation ticket. The actual implementation may vary as we start working on it.
Please check #5 first for any updates in interface and params.

The worker addresses will perform the actual transaction, so they must be unlocked before.
This function will perform the following.

• Get the encrypted_account from Config for the given address.
• Read the password from the env variable.
• Decrypt the account.
• Add it to web3 account wallet.

The password should be available in the environment variable. The key will be in the format MOSAIC_ADDRESS_PASSW_<address>. This is a proposal, the implementer can improvise.