Use uint64_t for fingerprints to prevent easy overflows

Instead of using int for state/command/traits/components fingerprints,
use uint64_t and reserve the value of 0 as a special "ignore" whildcard
(instead of former -1).

Change-Id: I3b95b4a8f9f41a963486d31ca6632ec0738dd7e9
Reviewed-on: https://weave-review.googlesource.com/1793
Reviewed-by: Alex Vakulenko <avakulenko@google.com>