added ability to add middleware classes

[josephmancuso]

This PR adds the ability to add middleware "groups" which are just lists of middleware.

Previously we were only able to use middleware like this:

ROUTE_MIDDLEWARE = {
    'auth': 'app.http.middleware.AuthMiddleware.AuthMiddleware',
}

Now we can add a list group:

ROUTE_MIDDLEWARE = {
    'auth': 'app.http.middleware.AuthMiddleware.AuthMiddleware',
    'is.owner': [
        'app.http.middleware.AuthMiddleware.AuthMiddleware',
        'app.http.middleware.OwnerMiddleware.OwnerMiddleware',
    ] 
}

This will run all middleware in the list.

I'll need to make a new fix for 2.1 since this won't work. 2.1 uses new Class based middleware:

from app.http.middleware import AuthMiddleware, OwnerMiddleware

ROUTE_MIDDLEWARE = {
    'auth': AuthMiddleware,
    'is.owner': [
        AuthMiddleware,
        OwnerMiddleware,
    ] 
}

[coveralls]

Coverage increased (+0.2%) to 91.873% when pulling f4a49f7 on add-middleware-list into 698ac69 on master.