Fetching and Parsing Feeds

* Set dashboards#show as root_path for signed_in users
* Add Feedjira to Gemfile
* Add sources and feed_entries tables to database
* Add fetching and parsing methods to source and feed_entry models
* Show user.timeline on dashboards#show
* User can see sources#index
* User can add new sources
For instance it's hard to see the correlation between this line and the next, I think a factory object would help clarify that.