In addon:DisplayFrame(): Replaced self:GetRecipeTable() with self.recipe_list

In addon:DisplayFrame(): Replaced self:GetRecipeTable() with self.recipe_list
Renamed SetRecipeButtonTooltip() and ClearRecipeButtonTooltip() to SetButtonScripts() and ClearButtonScripts(), and put them in a do-block as implementation functions for RecipeList_Update().
Made Button_OnLeave(), Bar_OnEnter(), and Bar_OnLeave() functions for use in SetButtonScripts() so as not to continually create anonymous functions.
Added highlighting of the currently moused-over recipe in the list.