Improve ST Module's Monte Carlo sampling to handle large number of samplers

[jiangwen84]

Reason

When we use SamplerFullSolveMultiApp together with MultiAppCommandLineControl, the memory usage is linear increasing with the number of MC samplers. For 10 million or even larger samplers, the memory usage per process can reach more than 10 GB. The large memory is used to store the command line option strings and the dense matrix of sampling data.

Design

1. We need to have a better way to store the command line option string in an efficient way.
2. The dense matrix of sampling data needs to be distributed to each process.

Impact

Capability improvement and no impact on existing tests.