Added Gravatar support

Added support for Gravatar images to be loaded if a user does not have a banner image set.
The Gravatar requested will be 64 x 64px and will only be loaded if it is classed as having a PG rating.
If the user has no Gravatar the default image user-black_64.png will be used.
Added Gravatar support
Merge pull request #117 from Numan1617/patch-1

Added Gravatar support