#1982 - Add placeholder for albums with no album cover.
- Added missing_album_cover.jpg placeholder image.
- Modified the graphics helper to use it.  Calling graphics::generate will copy it.
- Modified item::remove_album_cover and gallery_event::item_created to run graphics::generate.
- Added unit test to Graphics_Helper_Test.
Merge pull request #115 from shadlaws/fix_1982

#1982 - Add placeholder for albums with no album cover.