forc wallet should always demand proper prefixing

[SilentCicero]

Abstract

Right now, the forc wallet plugin allows for non-prefixed hex strings. This should be disallowed and a clear error thrown. All hex data should come properly prefixed with a 0x. If possible, we should always strive for one proper way to do things in tooling.

This restriction will also prevent someone from accidentally pasting in data that may not be proper hex data and thinking its a key, for example.