Support for extended attributes (xattr)

[overheadhunter]

Once cryptomator/cryptofs#47 is fixed, we can support xattrs. Regarding error codes, we should stick to the osx manpage, which has a more detailed distinction between different errors.

Noteworthy: E2BIG and ENAMETOOLONG should be handled correctly, since the size might increase due to the encryption layer.

[infeo]

Closed in 2cb7a28

Once cryptomator/cryptofs#47 is fixed, we can support xattrs

Since this is a different project, we already implemented in this layer the xattr support, but return the "ENOTSUP" if the underlying java filesystem not support UserDefinedAttributeView.