Fix Database Insert Error Handling

[jpcunningh]

This is an update to #3751 to provide an error back to the client when database inserts fail.

[jpcunningh]

I'm testing the error code and will post here when complete.

[jpcunningh]

@PieterGit, this appears to be working for me.

[PieterGit]

@jpcunningh LGTM. I assume the trace with linenumbers will be visible in the console log, so that you can identify the exact exception. Most of the error lines have the exact same text. Let's see if @sulkaharo or @jasoncalabrese have time to review it. If people report mongo errors at https://gitter.im/nightscout/public we can ask them to test the new code. I'll merge to dev if no response within a week, because it's a small fix that looks ok. Did you test with a full mongodb?

[jpcunningh]

@PieterGit, good catch. I modified to have unique error log messages.

Rather than fill up my production mongodb, I made a test branch that programmatically forced an "error" so it flowed through the rest of the data flow to the client.

I'm not sure how long it will be before my database naturally fills up again. It's probably in the range of 2-3 weeks.

[PieterGit]

Merged to dev. If there is somebody on https://gitter.im/nightscout/public with a full MongoDB we'll ask to test this new feature.

[PieterGit]

The user documentation for this feature can be improved. I logged issue nightscout/documentation#2 for that.