Changes many fields to required -- as far as we were able to figure out,
signing would fail if these fields aren't provided anyway, so this
should not pose a compatibility problem.
Co-authored-by: matejcik <ja@matejcik.cz>
The maximum amount is defined in [Ripple's docs](https://xrpl.org/basic-data-types.html#currencies) but it's most likely in XRP and not in drops ("satoshi" equivalent). This commit increase the value to the drops equivalent.
closes#327
