* Move GenesisDocProvider and DefaultGenesisDocProviderFunc
GenesisDocProvider, being a provider of *types.GenesisDoc, makes sense
to be part of the types package.
DefaultGenesisDocProviderFunc, which relies on *config.Config to produce
a types.GenesisDocProvider, makes sense being part of the config
package.
* Add aliases to avoid breaking node package API
* Revert to original structure
After discussion, it appears as though the best place for the relocated
structures is still in the node package. This means that for the v0.31.6
release and into the future, there will be no changes two these two
entities' APIs.