Plugin for testing ad layout

This plugin uses the UAPPlugin framework to output ad content. However,
its ad content is just images with one red pixel stretched to the
right size. It's mostly useful for debugging theme layout.

To use this plugin, set the parameter for the ad size you want to use
to true (or anything non-null).

Example
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To make a leaderboard:

addPlugin('BlankAd', array('leaderboard' => true));
