Fix advanced search form error after JSF upgrade from 1.12 to 1.13

When deploying Nuxeo 5.4.0 on jboss EAP 5.1.0 or 5.1.1 (includes a JSF upgrade version from 1.12 to 1.13), the advanced search form crashes because of the converter set on the boolean checkbox for deleted documents inclusion.

See also NXP-5813 and NXP-5300 for changes: the boolean checkbox renderer is overriden in Nuxeo so that it can accept a converter (as any standard JSF component). The checkbox component behaviour has changed: it now sets a boolean sumiitted value instead of a string => need to update the renderer behaviour for this use case and avoid the following stack error:

Caused by: java.lang.ClassCastException: java.lang.Boolean cannot be cast to java.lang.String
at org.nuxeo.ecm.platform.ui.web.renderer.NXCheckboxRenderer.getConvertedValue(NXCheckboxRenderer.java:49)
at javax.faces.component.UIInput.getConvertedValue(UIInput.java:942)
at javax.faces.component.UIInput.validate(UIInput.java:868)
at javax.faces.component.UIInput.executeValidate(UIInput.java:1072)
at javax.faces.component.UIInput.processValidators(UIInput.java:672)