Reduce number of functions in the Authorizer

[nventuro]

The current iteration simply inherits AccessControl, which has grantRole and revokeRole, and adds batched versions (grantRoles(roles[], user), grantRolesToMany(roles[], users[], same for revoking).

With #980, we can now also add and revoke roles globally. I argue that having so many functions is a) error-prone both during development and when using the contract, and b) not really necessary, since we can always have batching at the caller level. For example, the current admin account is a Gnosis Safe multisig, which natively supports this.

We'll already introduce changes to AccessControl in #985: I propose we also do away with grantRole(role, account) and grantRoleToMany(roles[], accounts[]), and just keep grantRoles(roles[], where[], account) and grantRolesGlobally(roles[], account) (same for revoke).