Thumbnails

Pull request for fixing issue #51. The following changes were made:

* Added new thumbnails (as requested)
* Fixed typo in the Edmonton Public Art page (and related assets)
* Increased the limit of how many case studies are shown on the work page [(raised from 15 to 20)](https://github.com/l1f7/l1f7.github.io/blob/thumbnails/work/index.html#L18)