[WIP] Improve error-handling of mongo shell

[StephenWeatherford]

1. Rewrite interaction with Mongo shell - this especially should provide accurate error messages instead of "timed out" when the "use db" command fails.
2. Added mongo.shell.args configuration
3. Some minor cleanup/improvements

Close to finished, sending up the PR early get feedback on the approach. Ideally I'd like to write some tests, too. Rewrote shell.ts completely from scratch after Eric's comments from previous PR.

Fixes #838
Also fixes #1104

Possibly fixes error reporting for:
#1071
#988
#852
#820
#794
#1092

Testcases in OneNote:

[ejizba]

Generally a bit wary of all the debounce, setTimeout, etc. code in InteractiveChildProcess (what does await delay(0) even do??) but looks good overall so far. Will wait to do a more thorough review until you say it's ready.

[StephenWeatherford]

Generally a bit wary of all the debounce, setTimeout, etc. code in InteractiveChildProcess (what does await delay(0) even do??) but looks good overall so far. Will wait to do a more thorough review until you say it's ready.

Yeah, not happy about it, either, am open to suggestions.

setTimeout(fn, 0) is essentially "execute on next event loop" in Node.js (http://voidcanvas.com/setimmediate-vs-nexttick-vs-settimeout/ - overly complicated). Shouldn't matter what delay I use, I just have to give the stream time to process.