PHPCS fixes
Fixed problem with coveraging everything and not only src directory
Added http library to dependencies

Using Symfony Http Foundation
Added a Response wrapper to fix invalid headers with cgi based server
Moved Response class to Http directory

Signed-off-by: Piotr Biedruna <pbiedruna@leroymerlin.pl>
Fixed response namespace
Excluding http response wrapper from tests
Fixed typo in exception name
Added method to generate random sha1 hash values
A fallback filesystem class + tests
New methods in Source interface

Added interface methods to Filesystem' source classes
Throwing an exception on no sources when trying to get image without sources
Handling not found image
Handling image retrieving from sources
Hash filtering object
Function for content retrieval
Added a function to generate random string
Filesystem image object + tests
Filesystem image further tests
Filesystem source handling
Changed the idea behing fallback filesystem source

- Source is initialized with a single image object
- Tests were changed to facilitete change of architecture