Fix missing content and other bugs

\cc @commuterjoy 
My working theory is that theres a little bit of a delay between articles being published and appearing in the search API. So, searching for articles in the last 3 minutes (as was done before) might lead to articles being missed. Trying this out on Heroku to see what happens.

- Also improved the collection of tags from article
- Encode URI to fix notifications for things with spaces.