Refs #8594 Catch bad lexical cast.

The original code could cause an (effectively) infinite loop when a bad file
format was used.
Refs #8594 Convert output of LoadDaveGrp to histogram data.
Refs #8594 Update unit test to match output.
Refs #8594 Throw runtime error instead.

This is so that we can catch the error if setRethrows is set to true.
Refs #8594 Make the conversion optional.
Refs #8594 Update unit tests.
Merge remote-tracking branch 'origin/feature/8594_add_convert2hist_to_LoadDaveGrp'