add initial search in shared files
divide ids into chunks of 1k
return fixed path, skip shared files outside of 'files'
fix getAll(), refactor search by mime & search
add all results, sharing cache also returns entries for shared files in external storages
same for search by mime
adding PHPDoc comments to getBackend
ensure getChildren() is called on an instance of Share_Backend_Collection
Merge pull request #4207 from owncloud/search_shared_files

add initial search in shared files