fix(date):  invert timezone sign and always display sign

This commit fixes #1261 and #1532. This covers
two separate issues:

- Positive timezones were being formatted without
a leading `+` resulting in a formatting string
like: "HH:MM:ssZ" giving "12:13:141000" instead
of "12:13:14+1000". Fixed by checking if timezone
is > 0 and adding a leading "+".

- Timezone output signs were inverted.
mock.TzDate expects the timezone _offset_ as it's
first argument, _not_ the timezone. This means
that a mock.TzDate with a positive offset should
result in a date string with a negative timezone,
and vice-versa.

Closes #1261, #1532
fix($cookies): set cookies on Safari&IE when base[href] is undefined

Safari and IE don't like being told to store cookies with path set to
undefined. This change ensures that if base[href] (from which cookie path
is derived) is undefined then the cookie path defaults to ''.

The test verifies that the cookie is set instead of checking that cookie has correct path,
this is due to that cookie meta information is not avabile once the cookie is set.

Closes #1190, #1191