Make repeats/2 and repeat_on//1 steadfast

template_applicable/2 calls repeats(Task,"") to ask "Does this task
have no repetition rule?"  Because the two child goals weren't
steadfast, providing "" as an argument changed their behavior.  To
make them steadfast, we must bind an intermediate variable, then cut,
then bind the output variable.  Otherwise, the initially bound output
argument influences the goals' behavior.
Copy repeating tasks into Today

Only a few simple repetition rules are currently recognized.
Debugging messages indicate which ones aren't, so I can add support as
needed.
Rework padded_integer//2

The old logic was convoluted, hard to understand and didn't handle
zero values correctly.  The new logic is more declarative, easier to
understand, has tests and passes them all.

Both count//2 and lazy_plus/3 will eventually be factored out to a DCG
utility library and lazy predicates library, respectively.
Fix type error that broke due dates

JSON values are atoms but the rfc3339 form requires a codes argument.
Because JSON values are not well typed, compile time type checks
wouldn't have caught this problem.  Run time type checks would have
caught it and given a useful stack trace, so that would have been
helpful.