Random Data Generator updates

Add the ability to generate random character data that can be used by
stages that expect the cache to contain Strings. The data is still
written as an array of bytes, so stages will have to coerce the data to
a string value.
Improve random data generator and load file stages

RandomDataStage - improve the algorithm used to generate the random
string data. Also write String values to the cache when generating
random string data.

LoadFileStage - provide a property to write data from the file as String
values in the cache.