[MODERATION] organization blocking a user (#802)

- Resolves #476
- Follow up for: #540
- Ensure that the doer and blocked person cannot follow each other.
- Ensure that the block person cannot watch doer's repositories.
- Add unblock button to the blocked user list.
- Add blocked since information to the blocked user list.
- Add extra testing to moderation code.
- Blocked user will unwatch doer's owned repository upon blocking.
- Add flash messages to let the user know the block/unblock action was successful.
- Add "You haven't blocked any users" message.
- Add organization blocking a user.

Co-authored-by: Gusted <postmaster@gusted.xyz>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/802
(cherry picked from commit 0505a10421)

models/user/user_test.go

@@ -457,6 +457,12 @@ func TestFollowUser(t *testing.T) {
 
 	assert.NoError(t, user_model.FollowUser(db.DefaultContext, 2, 2))
 
+	// Blocked user.
+	assert.ErrorIs(t, user_model.ErrBlockedByUser, user_model.FollowUser(db.DefaultContext, 1, 4))
+	assert.ErrorIs(t, user_model.ErrBlockedByUser, user_model.FollowUser(db.DefaultContext, 4, 1))
+	unittest.AssertNotExistsBean(t, &user_model.Follow{UserID: 1, FollowID: 4})
+	unittest.AssertNotExistsBean(t, &user_model.Follow{UserID: 4, FollowID: 1})
+
 	unittest.CheckConsistencyFor(t, &user_model.User{})
 }