add server side validation to see if link will bring up a successful response.
modularize server side validation that checks if link will bring up a successful response.
change request validation to use request module instead of phantom because of speed and stability.
prevent user from adding same link twice
Merge branch 'master' of https://github.com/ReadUpCode/readup

Conflicts:
	app/controllers/items.js
Merge pull request #66 from DougKong/master

server side validation for adding a link