Add support for vertical offset of measurements

jirikadlec2[CodePlex]
In many research labs, the measurements are taken at different vertical levels

(for example water temperature at 2m, 10m, 20m depth ...)
The ODM database schema already facilitates this with the OffsetTypeID and OffsetValue in the DataValues table.

However, the Data chart and Data table doesn't plot the vertical offset.
Therefore if user selects a variable (temperature) and site then there are duplicate rows shown in the table.

The work-around solution is currently to label each vertical offset as a different site or as a different method.

Begin by tracing the Data chart and Data table, then inspect how DataValues.OffsetTypeID and OffsetValue are read. Confirm how vertical offsets should distinguish measurements in both views; done means measurements at different offsets no longer appear as duplicate rows or indistinguishable chart points.

Written by the indexing model from the issue text.