Reuse sessions with many origins

[szmarczak]

Fixes #17

[szmarczak]

The current implementation is bad because it requires another array for all sessions. Instead, we can move to something like this:

this.freeSessions = {
    [options]: [session]
};

To connect we need to do:

this.freeSessions[options].filter(session => {
    return session.originSet.includes(origin);
})

We get an array of sessions we can use.

[szmarczak]

Moved to #21