Fix and improve release-process.md

This commit adds a step, which is to git checkout the version to be
built. This ensures that the gitian-descriptors for said version will be
the correct ones. In addition, it updates the links for several
dependencies, where the previously existing links were dead.
Switch the order of win32 deps and win32 qt in release-process.md

release-process.md has the deps being built after qt. However, the descriptors for qt call for the deps file.
HTTPS-ify the downloads for the deps
Merge pull request #3028 from Michagogo/fix-dep-links

Fix and improve release-process.md