Revert "Delete COPYING"

This reverts commit f5117e72625c02d9d174453c6059685b65506c33.
Revert "Delete INSTALL"

This reverts commit 1d29b4943b7fb7a3cf6adc431db7833fb434a602.
Revert "Delete walletdb.h"

This reverts commit d89ed7e85aceef68e6616b4bbde00dfbb75e3270.
Revert "Delete wallet.h"

This reverts commit bacfbaf35e03c82c87e2e4606d860644db2c45cc.