ShutdownAppInsights() before/after all panics

[mereta]

Is your feature request related to a problem? Please describe.
If Retina panics AppInsights does not receive all relevant logs associated with the panic.

Describe the solution you'd like
Goal would be to ensure ShutdownAppInsights() before/after all panics. Relevant links:

• No way to catch errors from goroutines automatically golang/go#20161
• https://github.com/mitchellh/panicwrap

[mereta]

CC from #1203
#1203 (comment)