Create sftp.php

Adapter for SFTP using the pure php SSH library phpseclib
Update apps/files_external/appinfo/app.php

Adding support for SFTP
Update apps/files_external/lib/config.php

Adding support for SFTP mounts
Update apps/files_external/lib/sftp.php

Added checks for host keys and added exceptions thrown if constructor fails.
Update apps/files_external/lib/sftp.php

Added a little better exception handling, hopefully making it a little more robust
Update apps/files_external/lib/sftp.php

Added copyright notice
Added phpseclib to files_external as 3rdparty
Update apps/files_external/lib/sftp.php

Updated to using local 3rdparty + added a few missed braces.
Update apps/files_external/lib/sftp.php

Created test() function as per @pull/1031
Update lib/filestorage/common.php

Added function to clean a path
Update apps/files_external/lib/sftp.php

Added cleaning the root path
Merge remote-tracking branch 'upstream/master'

Conflicts:
	apps/files_external/lib/config.php
Update lib/filestorage/common.php

Small cleanup
check whether user belongs to the backend before calling getHome()
LDAP: do not store user home as it destroys configurability. always fetch it. use of cache is save however, it is cleared when settings are saved
code style
LDAP: version bump -> clean up database
LDAP: fix settings handling of homeFolderNamingRule option
Remove old OC4 link compatibility
keep track of trash bin size