ExportFilter Class obtains warning due to improper implementation of XMLGregorianCalendarImpl API

[dfcoffin]

Maven build generates the following warning when built with Java 1.7:

• /home/don/Git/greenbuttonalliance/OpenESPI-Common-java/src/main/java/org/greenbuttonalliance/espi/common/utils/ExportFilter.java:[154,9] XMLGregorianCalendarImpl is internal proprietary API and may be removed in a future release

[dfcoffin]

Oracle has stopped publishing the XMLGregorianCalendarImpl JAR file. Temporary fix to allow the project to build was to obtain latest version of source code and add it to the project.