Refine lateorders - error feedback, filter independence

Refine lateorders - error feedback, filter independence

Added error catching for bad user input on number of days.  I.E., if you
try to filter by "bAd", you now get an error message prompting for valid
digits.  Also I updated highlighting to use loop_context_vars.

Fixed filtering to work on either days, vendor or both.  Previously, if
you selected a number of days, you had to select a vendor or else got
empty results.  DOCUMENTATION NOTE: this supplies the expected behavior,
so specifying vendor is no longer required.

Changed filters form to GET method.

Signed-off-by: Joshua Ferraro <jmf@liblime.com>