We need to build some basic support tools into core

[JeffPyeBrook]

So many support request starts with teaching the person having the issue about WordPress debug and
log files. It would seem that with some very simple and light weight supprot tools, and some very selective logging it would make testing, debugging and supporting WPeC sites a bit easier for a large number of the issues that we encounter.

We need a few of things.

1. some simple support tools built into core, that do not slow down the system, and do not drastically increase the memory footprint of the site
2. some simple guidelines for developers about when to include simple diagnostic logging, when not to include it, and what to put into it
3. some simple administrator documentation on how to turn on/off the diagnostic tools and how to access the information they produce.

Started a little bit with pr #1787

[JustinSainton]

Related: #1035, #1036