Create BurnerRole.sol

[Ro5s]

Creates role for operator burns of tokens. For example, in the case of NFTs, tokens might represent certain certifications or other accreditation. There may be cases where a private key is lost and a central operator, such as a DAO, might then act to burn the balance at the lost address, or otherwise act to enforce rules associated with token registry.

[nventuro]

This is one of the reasons why I want to implement #1772.

We currently need a lot of boilerplate (the 40 lines of this PR) to define a new Role, and doing so is very error-prone. Since it doesn't make sense for us to host a bunch of roles which are essentially the same (except the names), we're left in a weird position where the roles we need are defined, but rolling your own is cumbersome.

Given this, I'd rather work on #1772 than keep adding roles like this one. @Ro5s would it be an issue for you to have your own BurnerRole in your project?

[Ro5s]

This makes sense to me! I realize after making the PR that I was basically just proposing a copy-paste of other roles with a slight adaption ERC20Burnable down flow to include operatorBurn function...... this can be seen in the following implementation of an NFT meant to certify Accred Investors.... making this all more modular is priority

[nventuro]

Alright then, closing in favor of #1772.