Introduce own manager for reduced model object

Move autocomplete functionality to own managers and add functions to
load reduced model objects by id

scm-webapp/src/main/java/sonia/scm/GenericDisplayManager.java

@@ -0,0 +1,42 @@
+package sonia.scm;
+
+import sonia.scm.search.SearchRequest;
+import sonia.scm.search.SearchUtil;
+
+import java.util.Collection;
+import java.util.Optional;
+import java.util.function.Function;
+
+import static java.util.Optional.ofNullable;
+import static sonia.scm.group.DisplayGroup.from;
+
+public abstract class GenericDisplayManager<D, T extends ReducedModelObject> implements DisplayManager<T> {
+
+  private final GenericDAO<D> dao;
+  private final Function<D, T> transform;
+
+  protected GenericDisplayManager(GenericDAO<D> dao, Function<D, T> transform) {
+    this.dao = dao;
+    this.transform = transform;
+  }
+
+  @Override
+  public Collection<T> autocomplete(String filter) {
+    checkPermission();
+    SearchRequest searchRequest = new SearchRequest(filter, true, DEFAULT_LIMIT);
+    return SearchUtil.search(
+      searchRequest,
+      dao.getAll(),
+      object -> matches(searchRequest, object)? transform.apply(object): null
+    );
+  }
+
+  protected abstract void checkPermission();
+
+  protected abstract boolean matches(SearchRequest searchRequest, D object);
+
+  @Override
+  public Optional<T> get(String id) {
+    return ofNullable(dao.get(id)).map(transform);
+  }
+}