Match icon colors of speech bubbles from the mocks.

Closes https://github.com/steffanc/Tahoe/issues/69.

Shrink 9 PNG's so they can be expanded.   9.png files can not be shrunk so we must start with a smaller size.

Create a SpeechBubbleIconGenerator to match colors of the speech bubbles.
Merge pull request #154 from rogerhu/69-fix-icon-colors

Match icon colors of speech bubbles from the mocks.