Create Whitelist contract inside access

[Alberto Cuesta Cañada]

Branch new/whitelist

This is a stripped down version of RBAC.sol, with just one Role.

An Ownable contract that keeps a mapping of address => bool

Methods:
isMember: returns mapping(address)
addMember: sets mapping(address) = true
removeMember: delete mapping(address)

There is no listing of members, that will be done in a separate issue and contract.

[Alberto Cuesta Cañada]

#58

[Alberto Cuesta Cañada]

I've noticed this is a copy of OpenZeppelin's Roles.sol. I need to work on it a little bit to see how we reference their work.