Rotated map images

Currently the `LayeredMap` component indirectly supports rotated maps, since the user can have transparent areas in the image where there is no data. However, directly supports rotation of images will reduce the data transfer needed (as transparent pixels outside region of interest is redundant).

Start by tracing the LayeredMap component's image input and its current handling of transparent areas. Define how directly rotated images should be represented and verify that redundant transparent pixels are no longer required, while preserving the map region of interest.

Written by the indexing model from the issue text.