Negotiate projection for image and tile layer sources

By renaming the setTileGrid method on the renderer to
negotiateSourceProjection, we can not only set the view's
projection on layer sources that do not require a specific
projection, but we also have a place for future efforts to
negotiate a suitable projection between the renderer and the
source.
Comment about setting resolutions for image layers

To keep the example simple, no resolutions are configured by
default. But a comment shows how to configure a set of
resolutions to reduce the number of requests for single image
layers.