Select or create shop before parsing

A shop map was created to group URLs by shops and process them in order. Now
that we have Amazon and each URL can be parsed independently, there is no need
to group them anymore. Moreover, shops were passed as an argument to the
handleProducts function. Shop name can be deduced by the parser itself. The
parser has a reference to the database. The parser now select or create the shop
before parsing products.

Signed-off-by: Julien Riou <julien@riou.xyz>

parser.go

@@ -10,6 +10,7 @@ import (
 type Parser interface {
 	Parse() ([]*Product, error)
 	String() string
+	ShopName() (string, error)
 }
 
 // filterInclusive returns a list of products matching the include regex