Add Support for Multi-Level Logging Components / Namespaces

[jblz]

...to be able to more-easily identify that the debug log came from e.g. the HTTP Client module

We could drill in via Query Monitor like this:

[chriszarate]

The "component" in the screenshot is automatically computed by Query Monitor and is intended to represent the plugin, mu-plugin, or theme that triggered the message. It is filterable, but that filter does not have access to the log message or its context.

I've made some related improvements in #154