OpenBVE v1.7.0.3

Version 1.7.0.3

Another small patch release (sorry!), updating one language file and the dependencies for the Debian package, solving an issue on systems which did not have mono-complete installed.

Please also note that this bumps the minimum Mono version required for Debian to 5.20- This is available in the current stable and newer by default. Alternatively, Mono provide their own repository for all currently supported Debian / Ubuntu versions.