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
Staticize a local constant
OXZ removal, make install-reported version accurate
Colour-code install menu by installability
Finish off basic interface, a bit of cleanup
Fix two bugs, one regarding equipment with requires_cargo_space set when fully loaded with cargo and one about misreporting available cargo space when fully loaded and with equipment requiring cargo space present.
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