Add delegator to contract calls

[Valazan]

Setting delegation when a smart contract is called

This PR allows to set a delegator when a smart contract is called:

e.g.

const transferResult = await contract.transact.transfer(
    '0x9e7911de289c3c856ce7f421034f66b6cde49c39',
    10000,
    {
        delegatorPrivateKey: delegatorAccount.privateKey
    }
);

[github-actions[bot]]

Test Coverage

Summary

Lines	Statements	Branches	Functions
	99.96% (3106/3107)	100% (657/657)	100% (647/647)

Title	Tests	Skipped	Failures	Errors	Time
core	463	0 :zzz:	0 :x:	0 :fire:	1m 4s :stopwatch:
network	589	0 :zzz:	0 :x:	0 :fire:	3m 31s :stopwatch:
errors	48	0 :zzz:	0 :x:	0 :fire:	14.789s :stopwatch: