Add a primary color toolbar style
Add a primary color toolbar style

In order to keep the look and feel of the offline areas page in line with the
rest of the app's UIs, I've added a new toolbar style that uses the app's
primary colors. Now we can retain a 'darker' theme for the offline areas page,
while ensuring the color pallette is in keeping with the rest of the UI.

google/ground-android,google/ground-android,google/ground-android