Update docker/windows toolchain and install cerbero deps
I have more fixes in the pipeline (for #39 (closed)), but The git update is very important because of https://github.blog/2019-12-10-multiple-git-vulnerabilities-in-2-24-and-older/
docker/windows: Download Python installer as python3-installer Having a binary called 'python3' anywhere that might accidentally end up in PATH is asking for trouble.
docker/windows: Install Python to a path without spaces This is needed for Cerbero since Autotools cannot handle paths to binaries that have spaces in them.
docker/windows: Use load-balancing for sourceforge URLs Instead of using a specific mirror, which may be slow or might disappear.
docker/windows: Update python, git, and MSYS2 The git update is particularly important because of security vulnerabilities on Windows related to NTFS.
docker/windows: Clarify some MSYS2 install steps
docker/windows: Fix 7zip extract command for MSYS2 -Wait is only needed for Start-Process. Also, explicitly extract the tar file into C:\ -- don't assume the current directory is C:\
docker/windows: Install CMake and WiX for Cerbero
docker/windows: Download and install MSYS for Cerbero