Improve poor handling of SteamVR crash

### Bug report:

TLDR: If SteamVR crashes for whatever reason, it is impossible to restart SteamVR and ALVR while wearing headset. Also there are orphaned Chrome processes made by ALVR.

#### How to reproduce

1. Start ALVR. SteamVR will automatically start.
2. Wait for SteamVR to crash (it usually happens once in two hours for me). Or just kill "VR Server" (vrserver.exe) via task manager. In windows task manager it is "End task" option from context menu.

##### Bad things which happen next:
1. On PC SteamVR will show window "SteamVR has encountered critical error" with options to restart SteamVR or quit SteamVR. No matter which option you choose, other bad things listed below still happen.
2. It would be impossible to restart SteamVR via "Restart SteamVR" button in ALVR window on PC. The button does nothing. ALVR web interface in Oculus Browser becomes inacessible too.
3. Because of things mentioned above it is impossible to make ALVR and SteamVR running properly again while wearing headset. The only way to do it is to put headset off, go to PC, close SteamVR, close ALVR, start ALVR again. For me it is very inconvenient because my PC is located in another room on another floor.
4. There also will be orphaned tree of Chrome processes (started by ALVR) that can only be killed manually via task manager or via PC restart. They will not be killed on closing ALVR or restarting SteamVR, etc. These trees can accumulate with multiple crashes.

Here is a screenshot of process hacker task manager showing a tree of ALVR chrome processes with parent "vrserver.exe" before SteamVR crash:
After SteamVR crash they are orphaned:

#### Environement

> What hardware do you have: CPU, GPU, Audio

Ryzen 2700x, GTX 1070, ur28m sound card

> What version of ALVR and SteamVR have you tried.

ALVR 15.1.0, SteamVR 1.16.10

> Do you have the latest Windows updates? Run "winver" in Windows 10 to get the version number

Windows 10, Version 2004