Add comments about the need of cache LRU

Passepartout/Sources/Model/Profiles/InfrastructureCache.swift

@@ -25,6 +25,8 @@
 
 import Foundation
 
+// TODO: retain max N pool models at a time (LRU)
+
 public class InfrastructureCache {
     public static let shared = InfrastructureCache()
     

Passepartout/Sources/Services/InfrastructureFactory.swift

@@ -28,6 +28,8 @@ import SwiftyBeaver
 
 private let log = SwiftyBeaver.self
 
+// TODO: retain max N infrastructures at a time (LRU)
+
 public class InfrastructureFactory {
     private static func embedded(withName name: Infrastructure.Name) -> Infrastructure {
         guard let url = name.bundleURL else {