Added new role user_image to set a User's Account Image

Users provide their own jpeg in the root of their xc-custom and set
image_path in their all.yml, the role takes care of the rest.  It also
backs up the existing image in case it had already been customized.

2nd attempt, switched from files to templates per rricard's suggestion
Merge pull request #15 from ninjabong/user_image

Added new role user_image to set a User's Account Image