Tiled Gallery: No need to wait for all images to load before resize anymore, since images know their dimension to begin with.
Tiled Gallery: Refactored the Tiled Gallery prototype to represent a single tiled gallery as the name implies, and added a separate prototype to represent a collection of tiled galleries. This way it's clear which operations are done for individual galleries and which are done for all.
Tiled Gallery: Extracted original-width and original-height attribute setting out of the resize function, and moved the call from resize to the constructor, since there is no need to see if the attributes are set in every resize call.
Tiled Gallery: Minor refactoring to maybeSetSizeAttributes.