User Root Resource: Use CDI Provider for subresources.

Resources are request scoped and we need only one sub resource per
request. That is, injecting all subresources (and their transitive
inejctions)in the constructor builds a lot of objects that are never
used.

Solution: Inject provider, that lazily inject the needed subresources
on demand.

scm-webapp/src/main/java/sonia/scm/api/v2/resources/UserRootResource.java

@@ -2,28 +2,30 @@ package sonia.scm.api.v2.resources;
 
 import com.google.inject.Inject;
 
+import javax.inject.Provider;
 import javax.ws.rs.Path;
 
 @Path(UserRootResource.USERS_PATH_V2)
 public class UserRootResource {
 
   public static final String USERS_PATH_V2 = "v2/users/";
-  private final UserCollectionResource userCollectionResource;
-  private final UserResource userResource;
+  private final Provider<UserCollectionResource> userCollectionResource;
+  private final Provider<UserResource> userResource;
 
   @Inject
-  public UserRootResource(UserCollectionResource userCollectionResource, UserResource userResource) {
+  public UserRootResource(Provider<UserCollectionResource> userCollectionResource,
+                          Provider<UserResource> userResource) {
     this.userCollectionResource = userCollectionResource;
     this.userResource = userResource;
   }
 
   @Path("")
   public UserCollectionResource getUserCollectionResource() {
-    return userCollectionResource;
+    return userCollectionResource.get();
   }
 
   @Path("{id}")
   public UserResource getUserResource() {
-    return userResource;
+    return userResource.get();
   }
 }