Moving TabFolderLayout into SWT to have a single copy.

Fixes eclipse-platform/eclipse.platform.swt#1317

Author: deepika-u

ui/org.eclipse.pde.ui/src/org/eclipse/pde/internal/ui/preferences/EditorPreferencePage.java

@@ -25,6 +25,7 @@
 import org.eclipse.pde.internal.ui.editor.text.ColorManager;
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.layout.GridData;
+import org.eclipse.swt.layout.TabFolderLayout;
 import org.eclipse.swt.widgets.Button;
 import org.eclipse.swt.widgets.Composite;
 import org.eclipse.swt.widgets.Control;