ARQGRA-224: page fragments implementing WebElement interface delegate

interface invocations to Root

* A Page Fragment can be declated asbtract when implementing WebElement
  interface. Then all method invocations on such Page Fragment will be
  intercepted, and those which are from WebElement interface will be
  delegated to the Root of the page Fragment.
* LocationEnricher - the creation of the page object was improved, now
  it is using the method from PageObjectEnricher to do so
* Support for declaring Page Fragment as abstract class not added, cause
  it requires more changes in the code