Adding Rack in DC Visualization mode not saving

### Steps to reproduce

1. Go to Data Center > DC Visualization > Choose any server room
2. Click Edit
3. Click on a blank square/tile to add a rack
4. Fill in a name
5. You can add a description or leave it blank, makes no difference
6. Click save.

Nothing happens and you get the following error in the `ralph.log`:

`[29.04.2020 12:48:37,668] WARNING [MainProcess 1272] base - Not Found: /api/rack`

I tested this on the Ralph Demo site and got the same behaviour. Browser is Chrome 81.0.4044.122 (Official Build) (64-bit)

### Expected behavior

It should create the rack and then allow me to go and add other properties.

### Actual behavior

It doesn't save

### Environment

* Ralph version: 20200421.1
* Operating system: Ubuntu 18.04.4 LTS
* Method of installation: Deb package