Replacing Infura with IN3 Client.

**Description:**
Slock.it just released the first stable version of its blockchain client, INCUBED (IN3). INCUBED unlike Infura connects to the Ethereum Blockchain via an INcentivized Node Network which incentivizes and distributes the trust on remote nodes while still keeping the bandwidth and storage requirements low. Such a client fits the requirements of wallets like metamask.

**Problem:**
The codebase is huge and the project structure is new to me. If someone could explain the architecture in detail and point out the important sections of code that is responsible for the RPC communication it would be great. Also a brief explanation of the project structure would be a cherry on the top.

**Sidenote:**
Please feel free to voice your views on using IN3 with metamask. All suggestions are welcome.

**Links:**
* [Read the Docs](https://in3.readthedocs.io/en/latest/)
* [Release Blog](https://blog.slock.it/incubed-stable-release-c35b3a4ec10a)
* [How IN3 Works](http://how-in3-works.slock.it/)

Start with the project structure and RPC communication areas in the MetaMask extension, using the linked IN3 documentation and “How IN3 Works” material for context. Before implementation, clarify the architecture, integration scope, and views on replacing Infura; done would require an agreed plan or a defined IN3 integration rather than only an explanation.

Written by the indexing model from the issue text.