Added GetProfilePicture

Added functionality to retrieve a profile picture (thumbnail or full size).

Added GetJID($to) method which will always return a JID. This is to prevent accidental use of number instead of JID, or adding whatsAppServer twice to a target which is already a JID.

Also added some minor fixes after looking in the issue tracker and added a number of methods from WhatsApiNet.

Updated testprotocol.php