Got the csv export working

I mostly just copied the code for the CSV output from the prototype, but
it took a little finagling to get it working right.  It seems to behave
properly now, though.  Cells with double quotes and commas get imported
correctly by excel.

I've also started, but haven't finished, a mechanism for extracting a
subset of the data from a record collection.  This will be used for
situations where the user has selected several rows in grid, and clicks
the spreadsheet button, which will output just those rows.

Also added:  Filesaver.js (for the "saveAs();" function.