XmlPath with arguments, test cases, bug fix in AssertionSupport

As promised this is the adaptation of XmlPath. Test cases in JsonPathTest and XmlPathTest are running smoothly plus I added test cases for expressions with parameters.
I fixed a bug in AssertionSupport. The startedWithDot check is unnecessary. If the pathFragment starts with a dot (e.g. ".find(a->a.name==b)") the pathFragment.split() will create an empty string at [0]: dotFragments=["", "find(a->a", "name==b)"]. When doing the dotFragments.join(".") the dot in the beginning is added again in the join of dotFragments[0] and dotFragments[1].
Without this bugfix my new test case does not run since two dots are inserted.