Fixes Issue #109 - Context root is appended twice when using Navigate.to() class

This is more like some observations I had regarding the problem and I don't think it's good as fix. I saw that when using ```Navigate.to("some-view-mappable-to-pattern.jsf")``` to workflow is something like:
```
 RewriteNavigationHandler.redirect()
  --> ExternalContext.encodeUrl()
    --> UrlMappingRuleAdaptor.perform()
      --> UrlMappingRuleAdaptor.rewritePrettyMappings() //here contextPath is prepended
```
So, contextPath might not be appended in different situations (where there's no mapping matched, or pretty-config used at all). I think the check in ```RewriteNavigationHandler.prependContextPath()``` actually comes with a problem, specifically when we have cases like _contextPath="/app"_ and _outbound="/applications.jsf"_. Also, doesn't seem right having contextPath managed in different or unrelated places.

What are your thoughts?