I've now moved most downloads & integrated the 4.9.3 and 5.2.0 releases.
Next steps are:
- update travis symlinks
- delete old folder structure

There's one small problem: The Travis links are currently in binaries/$HOST and these host folders should be removed at some point.

@Iain shall we move these symlinks to a new location? Maybe ftp.gdcproject.org/ci/gdc-x or ftp.gdcproject.org/binaries/ci/gdc-x ?