warning for incomplete coverage of value range in DQO accuracy table

[fawda123]

The value range column indicates a range of measurements within which DQOs apply for each parameter. It was assumed that users would supply value ranges that cover all possible outcomes for a parameter. This may not be true. MassWateR should return a warning on import and QC report generation (i.e., checkMWRacc() and qcMWRreview() or lesser functions) indicating incomplete value ranges and the associated parameter(s). This issue should be addressed after #57.

[fawda123]

Added utilMWRvaluerange() which checks for na, gaps, and overlap. checkMWRacc() returns a warning for gaps and errors for na and overlap.

[fawda123]

Warning now returned with tabMWRacc() (from qcMWRacc()), also returned when running qcMWRreview(), if gap is presentin Value Range column of the DQO accuracy file.

[fawda123]

@ben-wetherill this should have the correct behavior now, warnings are returned on import of the DQO accuracy file and on report generation if the DQO accuracy file has gaps in the Value Range column. Also note that readMWRacc() now also checks for overlap in value ranges (e.g., >4, <5), which will now return an error on import.

[ben-wetherill]

This looks good.