MetaMask Dev Mode

## Problem ##
As we continue to find ways of improving MetaMask for two user-types (devs & average users), we're seeing a lot of feature requests coming in for developer-specific needs and functionality (which we tend to focus on solving). This means a lot of the design resources are being allocated for adding features and solving ux problems for developers. As our user base continues to grow, we're quickly learning that the developer user-type is a small percentage of our user base (we should get actual metrics on active user-types).

As we continue to grow and prioritize the work we do and think about the people using MetaMask, how might continue to improve the ux and innovate for the "average user", while also not have design block dev-specific feature development?

## Proposal ##
We can start to think about MetaMask as two separate experiences, the "Light" version, and the "Pro" version.

#### MetaMask Light Version ####
Designed for the "90%" or "average user" that provides basic controls for interacting with web3.

#### MetaMask Pro Version ####
Designed for the "10% or "power user developer". Not blocked by design. Dev-specifics features can be pushed without much design consideration. It serves as a experimental sandbox for technical features to be tested etc.

## Benefits ##
- The design team for MM Light takes on a more user-centric design approach with a focus on improving the ux for the average user, improved design process, more robust ux research, usability testing and UX innovations on MetaMask product(s).
- Works with the subspoke model - we can have a 'MM Pro" team and the "MM Light" team.
- Deeper understanding of our users - cater features and designs to the right users as opposed to assuming all of users will benefit from features
- Developing for MetaMask Pro will no longer be blocked by design