Identicons: Add identicons to ChaOS Lab [3/3]

When enabled, new contacts will be assigned a unique
5x5 identicon as the contact photo instead of the boring
default one.

PS2:
Use the new GithubIdenticon class for now.

PS3:
Make use of the IdenticonFactory

PS4:
Add proper annotations for ChaOS Lab.

Change-Id: I8c166504571baf6acaacfb95eda33b13c14ffa61