Add support for EAN codes (EAN8, EAN13)

[AndreySV]

Loyalty cards with EAN13 codes are used a lot in my area. EAN8 and EAN13 can be covered by single format "EAN". The length can be automatically detected based on given digital code.

{
    "accentColor":"#ffed2c20",
    "app":"passandroid",
    "creator": "skvorl",
    "barCode":{
	"alternativeText":"",
	"format":"EAN",
	"message":"1234567890123"
    },
    "description":"Card",
    "fields":[
	{
	    "hide":false,
	    "label":"Card number",
	    "value":"1234 5678 9012 3"
	}
    ],
    "id":"8333331f-2a83-4d26-b212-c42a8a918333",
    "locations":[],
    "type":"LOYALTY",
    "validTimespans":[]
}

I've added implementation for my Passes (fork). It would be nice to have this format documented.