Handle invalid constraints

Invalid constraints should throw an error before reaching the web service and 400ing. 

Example: 

Invalid constraint: 

```
{:where {:id "BOB"}}
```

Valid: 
```
    {:where [{:op "="
     :path "Gene.id"
     :value BOB}]}
```

currently, imcljs merely ignores invalid constraint properties and converts them to `<constraint />`. This will always 400 in InterMine webservices. 
