Refactor to change from grid = TRUE/FALSE to ncpus for user to specify number of CPUs in analyzeData.

[MikeKSmith-Pfizer]

Back in 2006 when MSToolkit was developed, personal computers didn't generally have multiple cores available on the CPU, so we only implemented multiple CPU options if grid = TRUE.

Now we should change the option name to allow the user to specify a number of CPUs to use for analysis. For CRAN (see #18) we should set the default to 2. Or set default to an option called Ncpu (see Rdatatable/data.table#5658).

Should we assume that number of clusters = ncpus?