End the require mess

* 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
Bye Resque. Ohai Sidekiq.

* Dropped all references to Resque
* Moved all jobs under app/workers since that's the Sidekiq convention
* Renamed Jobs module to Worker to match new location
* Adapted all jobs to Sidekiq
* Replaced all enqueue calls with perform_async
* Dropped Resque hacks from specs and features, replaced with
  sidekig/testing in RSpec and sidekig/testing/inline in Cucumber
* Updated scripts to start a Sidekiq server
* Inline Sidekiq sinatra app
* Let Sidekiq create the actual Redis instance
* Workaround already initialized constant warnings in service models
* Resolved ToDo in one job definition by creating proper exception clases
  for some errors in receiving posts
* Added sidekiq section to configuration to make it completly
  configurable to the user
* Add Sidekiq middleware for clean backtraces
* Delay HttpMulti retry to give offline pods a chance to come back up
* Do not retry on GUID already taken and alike errors
* Be graceful about deleted posts in GatherOEmbedData
Merge pull request #3993 from MrZYX/sidekiq

Sidekiq (+ some cleanup)
Fix the tag number in sidekiq's changelog notes

... it's been a while ...
bump sidekiq and cleanup unicorn.rb
Add explanation to services index page. Closes #3064
Merge pull request #4095 from embs/feature/3064-add-services-explanation

Add explanation to services index page. Closes #3064
add app directory to the autoload paths so that the worker files are loaded in development mode too
Fix default image url in profiles table. Closes #3795
Merge pull request #4098 from embs/feature/3795-fix-default-profiles-image-url

Fix default image url in profiles table. Closes #3795