Settings page hangs and locks session if git command hangs

[isc-pbarton]

If a git command like ls-remote is hanging, the Git settings page will hang until it fails with a "Gateway Timeout" message. It also locks the session entirely. We should do some smarter async programming so that OS commands have a short timeout and display an error if they time out.

[isc-pbarton]

Ideally: all OS commands should be wrapped in a work queue manager process with a configurable timeout. Any commands called synchronously from the UI should have a short timeout. Any other commands should have a long default timeout that can be changed through settings.