add bower.json

In order to use this as a bower-package a bower.json is required (this PR adds one), and it is also required to register the package. (http://bower.io/)

Would be thankful if you could merge in and register as a package in bower:

bower register knockout-js-infinite-scroll https://github.com/thinkloop/knockout-js-infinite-scroll

(in case you do not have bower, you can install it by: npm install -g bower)