NEP-5 Token Contract API about neow3j

[gsmachado]

So, just adding more details about this issue:

High-level description:

• Implement the functionality described on #70.

Detailed description:

• Implement a wrapper class, like the ones implemented here or here.
• The wrapper class can be called "NEP5", where it needs to expose the same methods as described in the NEP-5 standard.
• Therefore, every time users call methods like .balanceOf() or .transfer(), the NEP5 class will internally either call the invoke RPC method or build a ContractInvocation object and perform the call to the given contract.
• The contract address/scripthash should be mandatory in order to construct the NEP5 class and start interacting with the contract

[Priyanshu-soni]

NEP3j lib is now updated for NEP-5 token contracts API, so we can now use The wrapper class "NEP5" with same methods as described in the NEP-5 standard