Start on OXZ manager.

Doesn't work at all...
For testing, download a test manifests.plist file

Currently only works synchronously, which is not very useful.
Xcode project update; format string fix
Use a real cache path for OXZ manager download
More work on the OXZ manager downloading the index.

- Make cache manager compile on GNUStep (was pickier about location of new public method)
- Prefix manifests cache file now it's in a shared folder
- Compatibility with missing protocol definition
Still doesn't download the file, though...
GNUstep doesn't have a working NSURLDownload so use NSURLConnection instead
Fix hard-coded cache path
Tidy up GNUstep cache folder selection

Select a sensible location for downloaded OXZs but don't do anything with it yet.
Add GUI for downloading manifests file
Some work on installer interface.
Allow installation of managed OXZs, adjust a few other bits
OXZ removal, make install-reported version accurate
Colour-code install menu by installability
Finish off basic interface, a bit of cleanup
Turn off debug logging, sort the installation list
Fix list scroll bugs, better sorting of lists, other UI fixes
A bit more in-manager documentation
Fix left/right keys in install/remove settings
Fix bug with failed download handling
Reverted previous commit and re-applied it the way cim intended it to be.