Mirroring display fails on some projectors

I use elementary as my primary OS on my laptop and desktop both. In general it works great, but there have been a few instances when I experienced some frustrations at times when I would expect them the least.

In the last few months I connected my laptop to four different projectors for talks using HDMI cable, but three of them did not allow me to mirror my display. Extended display mode worked fine though, but it was not ideal for the type of presentation I was giving. Those are wide projectors (most probably 16:9 aspect ratio). I am not sure if the problem is related to incompatible aspect ratio or sub-pixel scaling, but the experience should be smooth.

Later I was able to use custom `xrandr` commands to mirror on one of those projectors, but I am not sure how reliable that approach would be in future.

```
DELL Latitude 3570
elementary OS 0.4.1 Loki (64-bit)
Built on "Ubuntu 16.04.3 LTS"
Linux 4.13.0-38-generic
GTK+ 3.18.9
Dual-Core Intel® Core™ i7-6500U CPU @ 2.50GHz
Intel Corporation Sky Lake Integrated Graphics (rev 07)
NVIDIA Corporation GK208M [GeForce 920M] (rev a1)
16.2 GB memory
235.2 GB storage
```

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