added a SynologyFTP adapter
updated the tests
removed unused use statements
#324 fixed Adapter\Local::has return false with file_exists
Merge pull request #313 from kristianedlund/synology_ftp

added a SynologyFTP adapter
Fixed #328: SFTP and FTP setConnectionRoot is now consistent when failing.
Close ticket #322 copy and move operations in the mount manager between filesystems
Merge pull request #323 from Markcial/ticket_322

Close ticket #322
Make MountManager::copy use streams
Added @method phpdocs for default plugins
Loosened sabre/dav version restriction
Extracted plugin functionality and made the mount manager use it.
Move plugins variable to plugin trait.
Made the exception message of the NotSupportedVisibilityTrait more explicid
Removed default plugins.
Merged the extracted plugin feature
Merge pull request #325 from felipecwb/issue-324

#324 fixed Adapter\Local::has with file_exists