this should fix some errors when registering models

I think I found the cause of issue #118. The function checkAndTransformName() doesn't return a string, but an object. so there were two problems:

```
if (!(MODELS.get(key).contains(checkAndTransformName(name)))) {
    MODELS.get(key).set(name, model);
```

you do a check with an object as a key but then store the model with the original string. and when you retrieve it you do:

```
ret = MODELS.get(db).get(checkAndTransformName(name));
```

i.e. you use an object as a key but the model was stored in a different place, since the key was a string.
To make the behaviour more consistent I could either fix the use of checkAndTransformName() or remove it. Since I see that if the key is an object everything is put in the same Bucket by comp.HashTable, I think it's a bit more efficient to have a string key. I also removed the variable "key" from the create() method as it was always equal to "db".

There's another fix too. When adding a model with the sintax "db.from(name)", the model tableName was no longer a string but an object.