RemoteLinux: Add possibility to ignore missing files while deploying.

New "Ignore missing files" checkbox was added to "Upload files via SFTP"
and "Create tarball" deployment steps. If checked, missing files will
produce a warning instead of the error thus preventing deployment
process from failing.

Change-Id: I0c3032746fbaae60aef2345802fc02c9951ab386
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>