Enable Refreshing for 127.0.0.1 and localhost pages (in addition to file://)

It's not uncommon for a web developer to need to view their website through a
server. I thought about switching Refreshing from a Chrome page action to a
browser action so that developers could enable Refreshing even if they weren't
using file:// URLs, but decided that enabling the page action for 127.0.0.1 and
localhost would support most use cases. In the future, I might add an options
page that lets users specify additional hostnames for which they want the
Refreshing page action enabled.
improve pathname guessing

This refers to the pathname guessing in the popup.

Before, just stripped off the first seven characters. This worked specifically
for URLs prefixed with 'file://'. Now we use generic pathname extraction that
works on all URL types (using the DOM's url parsing).