Add import and export command - US 183

auth/cert.go

auth/privkey.go

dfssc/impexp.go

dfssc/main.go

dfssc/security/files.go

dfssc/user/config.go

dfssc/user/config_test.go

tests/impexp_test.go

tests/testdata/cert.pem

tests/testdata/key.pem