Add hidden counter to imgur

+ Add a counter to the random imgur page.
+ Added functionality to the ``c`` key to toggle the counter display.
+ Added functionality to the ``r`` key to reset the counter to default.
+ Added a new configuration option for a quote category to get the
  default 'highscore' from.

  This commit adds a small decreasing counter to the corner of the
  screen. Hidden by default, press ``c`` to toggle it.

  The counter will begin at highscore + 1, and will decrease with every
  new image. This is intended to be used during contests to see how many
  images one can cycle through before, for example, finding a picture of
  a cat. The counter can be reset using the ``r`` key.

  The highscore is automatically set at page load to the most recent
  quote added to the category specified in the configuration option.
  Therefore it is important that only numeric data is placed in that
  particular quote.

  The score will not reset to a new highscore automatically, and nor
  will a new highscore update the quote category.
merge