Nicer implementation of time sequence creator function
[1589]
Can now specify 'time' parameter as a date/time string in loadFile,
e.g.:

time = '2000-01-24 18:00:00 UTC'

Still need a way to specify a format for the date/time
string.  Right now it depends on whatever visad's DateTime class is
using for a format pattern.

[1589]