HTTP Store

[unaizorrilla]

Add a new store, and probably remove db store, that allow get feature/toggle information using http request to Esquio UI. This allow clientes to get with features but without access to configuration database, and reduce some security concerns related with direct access to configuration db and also multi-tenants apps.
Some interesting features of this store will be:

• Allow caching support using IDistributedCache
• Support api leys with different levesl of privileges ( ie, readonly mode )