HPCC-11358 Sort WUs by Total Thor Time for both 5.0 WUs and 4.x WUs

The Total Thor Time of 5.0 WUs is stored under Statistics/Statistic
[@desc='Total thor time']/@value. For 4.x WUs, it is under Timings/
Timing[@name='Total thor time']/@duration. To sort the WUs, this
fix preparses WUs data into a local tree. The local tree contains
the data needed for WUQuery. For 4.x WUs, the 'Total thor time'
data in Timings/Timing[@name='Total thor time']/@duration is
convered into Statistics/Statistic[@desc='Total thor time']/@value.

Signed-off-by: Kevin Wang kevin.wang@lexisnexis.com