* Extract post fetching logic from Reshare into
its own module
* raise proper error message when fetching fails
* raise proper error message when parent is still missing
We can't skip fetch failures or missing parents and
still need to retry them in case we're sent the parent
later on
* 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