the Obs method getValueAsString(Locale locale) needs improvement

I have two complaints about this method.

First, if the obs value is numeric, the string generated should respect the 'precise' property of the related ConceptNumeric.

Second, the default date formats shouldn't include commas by default – these are the default column separators in csv exports, and it makes this method less useful if you're designing a data export. I think for dates yyyy-MM-dd would be more generally useful.