closes #6310

closes #6223

This new class replaces all existing server side message
rendering helpers and is the new global entry point for such
needs. All models with relevant fields now expose an instance
of MessageRenderer for those. MessageRenderer acts as
gateway between the existing processing solutions for markdown,
mentions and tags and provides a very flexible interface for
all output needs. This makes the API to obtain a message
in a certain format clear. As a result of centralizing the
processing a lot of duplication is eliminated. Centralizing
the message processing also makes it clear where to change
its behaviour, add new representations and what options
are already available.

* Get rid of early pathname requirement
* Use require_relative where approciate
* Drop unused files
* Imported new application.rb, environment.rb and environments/* from fresh Rails app
* Cleaned up boot.rb
* Load config in boot.rb
* Deduplicate environments/integration*.rb
* Move username blacklist into defaults.yml
* Ruby 1.9 Hash syntax everywhere
* Reorganize lib/diaspora/markdownify to match conventions
* Get rid of full path requires where possible
* Add dummy content to production section diaspora.yml.example to prevent warning
* Drop sqlite? method
* Move postgres? method into ConfigurationMethods
* Drop token authentication from User

* 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