Support web3j for VM calls

[orogvany]

In order to function easily with the wide variety of existing development tools for VM, we should probably support the web3j API for semux.

[semuxgo]

We should at least consider providing minimum support for web3 clients, so existing toolset can be used.

[orogvany]

I think maybe we should move this to 1.6.0, as it's a large undertaking, and should require no fork, as its just API support.