Make the game work with AdBlock Plus

[AdBlock Plus](https://adblockplus.org/) suggests the [EasyList](https://easylist.adblockplus.org/en/) filter list by default. One of the filters in it blocks the string "/dblclick." for some asinine reason, and the file "/gfx/events/dblclick.png" matches this. 

This PR renames "dblclick.png" to "dclick.png" and introduces a little hack to load that file instead. Seems to work just fine on Chrome 34.