fixed contrib/gitian-descriptors for Linux 32, Linux 64, Windows 32 an OSX

- fixed contrib/gitian-descriptors for Linux 32, Linux 64, Windows 32 an OSX
- updated macdeploy/macdeployqtplus to latest bitcoin upstream
- updated release-process.md

known issues:
- setup.exe for Windows 32 is still branded as Litecoin
- test of upload of signatures to gitian.sigs pendig
- build system (makefile, darkcoin-qt.pro) is outdated and needs update to autotools/autoconf
- Windows 64 build not working due to linker issues
Well, as long as it's not merged yet, you can simply correct it in your branch, commit & push again. The PR will then automagically be updated