Blender Git Loki

Windows/MSI: Rework MSI installer.

The installer always upgraded the last version installed and did not allow for two versions to be installed side by side.

The reworked installer will allow side by side installs

install order:
```
2.81 -> 2.81a -> 2.82 : Allowed , will result in both 2.82 and 2.81a being installed
2.82 -> 2.81 -> 2.81a : Allowed , will result in both 2.82 and 2.81a being installed
2.82 -> 2.81a : Allowed , will result in both 2.82 and 2.81a being installed
2.82 -> 2.81a -> 2.81 : Not Allowed, 2.81 will only install if you manually remove 2.81a first.
```

Do note though that this will not apply to any previously issued installers and even for 2.80a this is not something we can fix.

This patch is for landing in 2.81 *only* and should be excluded from any possible 2.80a release.

Second change is a change to the compression level, building the MSI takes 30 minutes, which is crazy, perhaps worth it if the compression actually pays of.

```
MSI - none 1:35 247.0 MB (260,025,634 bytes)
MSI - mszip 2:02 89.6 MB ( 94,022,946 bytes)
MSI - low 2:35 81.6 MB ( 85,646,626 bytes)
MSI - medium 4:11 77.3 MB ( 81,136,930 bytes)
MSI - high 28:01 74.7 MB ( 78,384,418 bytes)

zip 1:32 93.2 MB ( 97,732,293 bytes)
7Z 2:22 65.0 MB ( 68,171,614 bytes)
```

It didn't, so I lowered it to medium, seemed reasonable.

Differential Revision: https://developer.blender.org/D5494

Reviewers: brecht, jesterking