Moves backbone.babysitter and backbone.wreqr to devDependencies

Since `lib/backbone.marionette.js` includes both babysitter and wreqr there's no need to have them in the dependencies.
ATM they get installed as separate components side-by-side with backbone.marionette. If a developer's not attentive she'll include those in their html too.
And if a developer chooses to use the `core` versions instead, she'll know she needs to bower install those, or link the ones in `public`.