Don't expose termsAndConditionsAgreedAt

1. Don't expose `termsAndConditionsAgreedAt` as input param, because of ..why?
2. Make the `termsAndConditionsAgreedVersion` a *required* input param
   for `SignupVerification`. If new users register, they have to confirm
   the terms and conditions. I added another test to check what happens if
   the user sends `null`.
3. Sorry @ogerly for confusing you with my review here:
   https://github.com/Human-Connection/Human-Connection/pull/1556#pullrequestreview-287516516
   What I meant is that we want to simulate a user with no
   `termsAndConditionsAgreedVersion`. But of course the `variables` must
   have it set when you run the mutations. Now we have the
   exclamation mark in the input param, see point 1 ☝️

backend/src/schema/resolvers/registration.spec.js

@@ -62,7 +62,7 @@ describe('CreateInvitationCode', () => {
         name: 'Inviter',
         email: 'inviter@example.org',
         password: '1234',
-        termsAndConditionsAgreedVersion: '0.0.1',
+        termsAndConditionsAgreedVersion: null,
       })
       authenticatedUser = await user.toJson()
     })
@@ -352,8 +352,7 @@ describe('SignupVerification', () => {
         name: 'John Doe',
         password: '123',
         email: 'john@example.org',
-        termsAndConditionsAgreedVersion: null,
-        termsAndConditionsAgreedAt: null,
+        termsAndConditionsAgreedVersion: '0.1.0',
       }
     })
 
@@ -446,6 +445,16 @@ describe('SignupVerification', () => {
             expect(emails).toHaveLength(1)
           })
 
+          it('updates termsAndConditionsAgreedVersion', async () => {
+            await expect(mutate({ mutation, variables })).resolves.toMatchObject({
+              data: {
+                SignupVerification: expect.objectContaining({
+                  termsAndConditionsAgreedVersion: '0.1.0',
+                }),
+              },
+            })
+          })
+
           it('updates termsAndConditionsAgreedAt', async () => {
             await expect(mutate({ mutation, variables })).resolves.toMatchObject({
               data: {
@@ -456,6 +465,18 @@ describe('SignupVerification', () => {
             })
           })
 
+          it('rejects if version of terms and conditions is missing', async () => {
+            variables = { ...variables, termsAndConditionsAgreedVersion: null }
+            await expect(mutate({ mutation, variables })).resolves.toMatchObject({
+              errors: [
+                {
+                  message:
+                    'Variable "$termsAndConditionsAgreedVersion" of non-null type "String!" must not be null.',
+                },
+              ],
+            })
+          })
+
           it('rejects if version of terms and conditions has wrong format', async () => {
             variables = { ...variables, termsAndConditionsAgreedVersion: 'invalid version format' }
             await expect(mutate({ mutation, variables })).resolves.toMatchObject({

backend/src/schema/types/type/EmailAddress.gql

@@ -18,7 +18,6 @@ type Mutation {
     avatarUpload: Upload
     locationName: String
     about: String
-    termsAndConditionsAgreedVersion: String
-    termsAndConditionsAgreedAt: String
+    termsAndConditionsAgreedVersion: String!
   ): User
 }