mediawiki.inspect: add method for grepping loaded modules

Example usage:

	>>> mw.inspect.grep(':hover .settings-text')
	["ext.uls.init"]
	>>> mw.inspect.grep('options.expire')
	["jquery.cookie", "mediawiki.user"]

Use cases:
* You're debugging a layout bug and want to trace a CSS rule to the module
  which inserts it.
* A JavaScript error contains a distinct and plausibly unique substring (such
  as a variable name), and you want to identify the module that is causing the
  error.

You can re-load the page with debug=1, but you still need to decipher load.php
URLs for non-file modules, and you might not be able to reproduce the issue in
debug mode. Alternately, you can grep a full clone of the production branch
that the wiki is running (assuming you have one handy), but that won't help you
if the module is a gadget.

Change-Id: Ie5f0e7d1c7022f8d399e895f157db8acefc8abee
(cherry picked from commit 5b9aa7cf4a06ab55f2eed1715fbdab834e2942a0)