* Add stringified payload to metametrics controller trackEvent error message
* Don't include full payload when throwing error on missing event or category in trackEvent
Attempts to send metrics would fail when no `options` were used. This
was because when the options parameter was not set, it was often sent
over our RPC connection as `undefined`, which gets serialized to `null`
when the message is converted to JSON. This `null` parameter didn't
trigger the default parameter set in the metametrics controller, as
default parameters are only used for `undefined`.
Instead the `options` parameter is now treated as fully optional, with
no default value set. The optional chaining operator is used to ensure
it won't blow up if it's not set. A fallback of `{}` was used for the
one destructure case as well.
