Network intercept functions, wait function, silence page errors

[dgendill]

5. Some initial work on the network interception functions of phantom.
6. When evaluating code on a page, if that page has errors unrelated to your own code, you'll see them in the console. For that reason, I've added a function to silence page errors.
7. For convenience I've added wait function to Page.
8. Since page.evaluate can return undefined, I check for that before accessing the type property.