add custom icons and assign to history avatars (by index)
User gets a random avatar if gravatar email is not set

[#97]
hive-gravatar renamed to hive-avatar
Move avatar related functions into hive-avatar & use them

[#97]
History page uses avatar.getAvatarByIndex

And settings page uses avatar.getAvatar
[#97]
Waggle uses stock avatar if gravatar is not set

[closes #97]
Merge branch 'avatars'