Namesys is a very useful submodule. Given a ValueStore and a Datastore it can
resolve and publish /ipns/ paths.
This functionality does not need to be sequestered inside go-ipfs as it can
and should be used without IPFS, for example, for implementing lightweight
IPNS publishing services or for resolving /ipns/ paths.
"keystore" extraction was necessary, as there is a dependency to it in
namesys. Keystore is also a useful module by itself within the stack.
Fixes#6537