Read signing info from gradle.properties.
Cleanup code around images. Add initial toolbar code.

This change stops activities from knowing about HighlightingImageView,
moves certain pieces of logic from the ImageView to ImageAyahUtils,
and makes the page scaling data cached across instances. It also
fixes a bug where highlighting data was slightly off after switching
orientations from landscape to portrait.

In addition, this commit adds the initial AyahToolBar class and related
display logic. The code to display this is commented out since it's not
done yet.