Add Sequelize options for CLS support

Added support for continuation-local-storage to the 1.7.0 branch.

I modified the CustomEventEmitter class to take a passed in CLS namespace and bind to it, if it exists.

The rest of the changes were to propagate a passed in CLS namespace from the Sequelize options to other dependent classes.

I hope someone finds this useful!
Could we condense these two options just to `cls`, the user has to provide a namespace to enable it, no need to have multiple options as far as i can tell? :)