Unify public link methods with private files ones

[PVince81]

Many methods are not consistent with the "fileManagement". For example in "fileManagement" downloading is done with getFileContents but in public link access it's done with download. Also, every method for public links require the token and public link password.

One possible solution is changing the concept of the SDK and have the same API signature regardless whether public or private, see https://github.com/owncloud/owncloud-sdk/issues/349#issuecomment-551601349