Add CredentialState

This to enable the individual key handling needed for #7.

feudal/backend/models/__init__.py

@@ -552,3 +552,32 @@ class NewDeploymentStateItem(models.Model):
             self.site,
             self.id,
         )
+
+
+class CredentialState(models.Model):
+    DEPLOYED = 'deployed'
+    NOT_DEPLOYED = 'not_deployed'
+
+    STATE_CHOICES = (
+        (DEPLOYED, 'Deployed'),
+        (NOT_DEPLOYED, 'Not deployed'),
+    )
+
+    state = models.CharField(
+        max_length=50,
+        choices=STATE_CHOICES,
+        default=NOT_DEPLOYED
+    )
+
+    credential = models.ForeignKey(
+        SSHPublicKey,
+        related_name='credential_states',
+        on_delete=models.SET_NULL,
+        null=True
+    )
+
+    target = models.ForeignKey(
+        NewDeploymentStateItem,
+        related_name='credential_states',
+        on_delete=models.CASCADE,
+    )