Slim 2.3
Add date & qte fields to purchases

* add date & qte fields to purchases of Purchase$getPurchasesForUser return
* rename User$getLastPurchase into User$getLastPurchases
Merge pull request #235 from trecouvr/slim-2-3

Slim 2.3
Merge pull request #238 from trecouvr/add-info-to-purchases

Add date & qte fields to purchases