Add ConsoleLogger, use it for eval.php -d

Add ConsoleLogger, use it for eval.php -d

eval.php previously set $wgDebugLogFile to /dev/stdout. This had the
following problems:

* It doesn't work if the maintenance script is executed via sudo, since
  /dev/stdout is typically owned by the original user, so MW can't open
  it. Using php://stdout worked on HHVM but not PHP.
* Setting $wgDebugLogFile has no effect if the wiki uses MonologSpi.
* Setting $wgDebugLogFile has no effect on channels configured with
  $wgDebugLogGroups.
* stderr is a more appropriate place to send logging output.
* Writing to configuration variables is discouraged.

So, add ConsoleSpi, which is a very simple logging service provider
which sends all messages to stderr. This should be suitable for
debugging with eval.php or shell.php in WMF production or beta.

Change-Id: Ib0d6ce45e0cbecd58263fc4e360c63d4149acb3a