Enhancement: Allow XmlTypeCheck for strings

This change allows that the class XmlTypeCheck can be used to
check strings as well as files. Therefore the constructor has
been extended to one further element that indicates if the
input to be checked is a file or a string.

The functionality is tested with php unit tests.

Change-Id: I7432a754a512e0324c171667c3eac9d8e7838e0e
Merge "Enhancement: Allow XmlTypeCheck for strings"