implement `export_all_types` flag in config
When developing a new aiken project, often we don't have all of the validators in place already. But we want to start building with some types that we will eventually use. Currently, we have to manually stub out validators so that aiken generates the blueprint with such types in place. This commit adds a new flag to the config that will cause aiken to generate the blueprint with all public types, even if they are not used in the project elsewhere. The warning message that is printed when no validators are found during compilation is muted when this flag is set.