BUG Report admin don't listen to filters

It seems like filter params that are added to the url are added in a bad way

Currently

    ?0[name]=filters[ContentReviewOwnerID]&0[value]=1

Expected:

    ?filters[ContentReviewOwnerID]=1
Added min stability for composer

Required for scrutinizer runs
Merge pull request #956 from stojg/reportadmin-bug

BUG Report admin don't listen to filters
Fixed behat image upload tests

Was using "File" class rather than "Image",
which broke HtmlEditorField->saveInto() with "unknown method getWidth()"
Fixed behat image upload tests (contd.)
Add PHP 5.6 to the test matrix