Prefix "/" before getResource(..) to prevent MalformedURLException

I get the following error on my first access to localhost:8080 :

```
Mapped exception to response: 500 (Internal Server Error)
javax.ws.rs.WebApplicationException: java.net.MalformedURLException: static/org/graphity/client/xsl/global-xhtml.xsl
        at org.graphity.client.provider.XSLTBuilderProvider.getXSLTBuilder(XSLTBuilderProvider.java:158)
        at org.graphity.client.provider.XSLTBuilderProvider.getContext(XSLTBuilderProvider.java:110)
        at org.graphity.client.provider.XSLTBuilderProvider.getContext(XSLTBuilderProvider.java:54)
...
Caused by: java.net.MalformedURLException: static/org/graphity/client/xsl/global-xhtml.xsl
        at org.eclipse.jetty.webapp.WebAppContext.getResource(WebAppContext.java:354)
        at org.eclipse.jetty.webapp.WebAppContext$Context.getResource(WebAppContext.java:1451)
        at org.graphity.client.provider.XSLTBuilderProvider.getSource(XSLTBuilderProvider.java:198)
        at org.graphity.client.provider.XSLTBuilderProvider.getSource(XSLTBuilderProvider.java:181)
        at org.graphity.client.provider.XSLTBuilderProvider.getXSLTBuilder(XSLTBuilderProvider.java:137)
```

(in Mac OS 10.10.1, Oracle JDK 8)

To resolve this error, I added the code that prefixes "/" before calling [getResource(filename)](http://docs.oracle.com/javaee/6/api/javax/servlet/ServletContext.html#getResource(java.lang.String)).