make defaults for groupBy configurable

We do not know which fields exist at compile time.
But it is a great help to have some pre-selected
fields in groupBy.
Solved by adding a configuration option.

pdb-ui/src/main/java/org/lucares/pdbui/domain/FilterDefaults.java

@@ -0,0 +1,33 @@
+package org.lucares.pdbui.domain;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+public class FilterDefaults {
+  private Set<String> groupBy;
+  
+  private List<String> fields;
+
+  public FilterDefaults(final List<String> fields, final Set<String> groupBy) {
+    this.fields = new ArrayList<String>(fields);
+    this.groupBy = new HashSet<String>(groupBy);
+  }
+
+  public Set<String> getGroupBy() {
+    return new HashSet<String>(groupBy);
+  }
+
+  public void setGroupBy(Set<String> groupBy) {
+    this.groupBy = new HashSet<String>(groupBy);
+  }
+
+  public List<String> getFields() {
+    return new ArrayList<String>(fields);
+  }
+
+  public void setFields(List<String> fields) {
+    this.fields = new ArrayList<String>(fields);
+  }
+}