Build system installer for Mullvad Browser on Windows

Currently Mullvad Browser inherits Tor Browse's portable-only installer on Windows. We should either:

1. Add support to existing installer to support portable OR system %PROGRAMFILES% installs
2. Create a second installer which can install to a system location, separate from the portable installer
3. Update existing installer to be a classic system installer and instead ship portable as a zip archive

Some things to consider:

• System installation requires Admin/Elevation privileges on Windows. NSIS installers can be built such that the elevation prompt happens automatically on launch, but this will likely/possible prevent portable installation on systems which the user does not have admin access (such as in library/univeristy/corporate terminals). I don't know if you can conditionally elevate in an NSIS installer based on install location.
• A second installer to counter the previous constraint would work, but could cause user confusion
• Providing a zip bundle may make it easier for dowstream package maintainers if any were to appear (eg for chocolatay)