Add Auto header detection to Populate_Metadata.py

[muhanadz]

I noticed that much of the work ome/omero-metadata#67 to create an auto header detecting method and allow NaNs was not propagated to the Populate_Metadata.py script.

This PR proposes adding this functionality such that the header type is automatically detected and "allow_nan" is an option.

To test, use a working CSV without header type defined such as:

image,dataset,ROI_Area,Channel_Index,Channel_Name
3659,1451,0.0469,1,DAPI
3686,1451,0.142,2,GFP-AuroraB
3746,1451,0.093,3,TRITC-edit

Without PR, all the columns should be StringColumn. With PR:

"ImageColumn",
"DatasetColumn",
"DoubleColumn",
"LongColumn",
"StringColumn",
"StringColumn"

if a #header row is defined in the CSV, it should always take precedence over the auto-detection.