Allow per-type scope-enum

## Expected Behavior

I'd like to limit the valid scopes on a per-type basis. For example, the `docs` type should accept `all` and each of my lerna packages as scopes, but the `build` type should perhaps accept only `npm`, `webpack`, `babel`.

## Current Behavior

I can specify valid types and valid scopes, but not tuples of which ones are valid together.

## Affected packages

* [ ] cli
* [x] core
* [ ] prompt
* [ ] config-angular

## Possible Solution

Allow one (or both) of `scopes-enum` and `types-enum` to accept an object instead of an array. Alternatively, introduce a new rule that accepts an object.