fixes #1476 

Collections from blocked servers are crippled so that the map still appears to attempt loading.

To test (for example):
* comment out the entry for catami.org from Config.groovy
* delete or cripple catami.org from the database
* add  the Catami layer, from the AUV platform
Those two can be taken from constants, declared at the head of this class. Also, can have better constants, such as `/dev/null` instead of `http://...` if it works. And instead of type `dummy`, we can go with `blocked`, or something.

So for instance this will be:
```
layerLink.server = {
    uri: this.BLOCKED_URI,
    type: this.BLOCKED_TYPE
};
```