closes #6465

Fixed tagFollowing not getting into preloads

* Rename and reorganize post fetcher to fix autoloading, also let it use
  Faradays default connection so we get nice redirects
* Add initializer to load libs at a central place
* added lib dir to autoload_once paths to increase thread safety
* Moved lib/exceptions.rb to lib/diaspora/ to conform namespacing

strip last beta leftovers and fix syntax errors, travis is kinda down, lets hope nothing breaks while I sleep

- `Rails.root` is a `Pathname`, so let's use `Rails.root.join`
- Clean up most of the remaining `File.join`s

DC DG; added LastThreeComments decorator so we don't have to load those comments when not needed (i.e. new profile pages)

and comment presenter