Allow the initial page to be specified when setting image inputs

[skjiisa]

Add initialPage: Int argument to setImageInputs and reloadScrollView.

This allows the image inputs to be changed after initialization while keeping position in the slideshow. For example, if the user gets toward the end of the slideshow, the app could load n more images, append them to the Image Inputs, unload n images from the beginning, then reload the inputs with setImageInputs, setting the initialPage to the current page minus n. This would allow the user to stay on the same image while having fewer images loaded, using less memory.

Also includes #385