Improve interpolation and store data as values

Improve interpolation function to work with sub arrays
Improve zip_data to work with arrays (with sub arrays) of different
lengths
parse_csv now converts some values to floats
This prevents many potential issues with string arithmetic later
Remove now obsolete parseFloat()
Add warnings fot working with extended timestamps (js number precision)
Fix verctorization of making ext and javascript timestamps
Hide date and time from plot variable table
Update demo to work with interpolation