Remove JQuery watermark plugin

[twagoo]

Previously (before VLO 4.x), the JQuery watermark plugin was used to show a placeholder value in the search/filter box of the facet panels. This has been superseded by an application of the Bootstrap placeholder attribute. Therefore the JS library and its usage can be removed:

• eu.clarin.cmdi.vlo.wicket.panels.search.FacetValuesPanel.java:

  target.appendJavaScript(
  String.format(
  "jQuery('#%1$s input').watermark('Type to search for more');", 
  getMarkupId()));

• vlo-web-app/src/main/js/eu/clarin/cmdi/vlo/wicket/pages/jquery.watermark-3.1.4 and its contents,
• the JQUERY_WATERMARK resource reference in JavaScriptReources.java and its usages.

[twagoo]

Reported by @wowasa