Abstract the SessionStore out of the Weboob source

Following !1188 (merged) the source (weboob.js) requires a knowledge of the models (the Access) to store its session. I feel like this is wrong.

I suggest we pass a dependency to the source when calling weboob.js with an object that will manage the session storage itself:

{
    saveSession: async session => {
        await Accesses.update(access.userId, access.id, {
            session: session
        });
    },
    deleteSession: async () => {},
    getSession: () => {}
}