Track rss, and add utm_source to each url that generated from feed.js

[nonumpa]

Fixes #222

Feature

1. Track subscriber number by sending event:
   Event Category: RSS
   Event Action: Subscribe
   Event Label: Source(Feedly, Feedrabbit, IFTTT)
   Document title: response header
   Document path: query variables

   Feedly

   • Sends subscriber number when subscribing.
   • Will cache the feed, it triggers the event when first time fetches the feed, and then each regular fetching(maybe once an hour).

   Feedrabbit

   • Sends subscriber number each regular fetching.
   • Triggers the event every time.

2. Track article page through google tag manager by adding utm_source
utm_source: Source(Feedly, Feedrabbit, IFTTT)
   utm_medium: RSS

Fix

1. Copy URL function shouldn't encode URL

Snapshots

Page title: res.header (subscriber number), Page path: query variables

utm_source to article page

[MrOrz]

Thanks for the update, it's looking good!

Some thoughts and questions appended.