Merge parameters to a new object

Description:
 - Merge new parameters to a new object always overriding the previous data.

Why:
 - Imagine the situation where you need to reload the grid using different filters,
merging into the first object (this.p), you are always appending data to the class parameters instead of override them

Bug sample:

```
this.p = {'postData': {'arguments': {'filter': {'username': 'john' }}}};
```

Once you call setGridParam again trying to "change" a parameter, in this case, filter, your object will be:

```
this.p = {'postData': {'arguments': {'filter': {'username': 'john', 'lastname': 'maria' }}}};
```

And if you call it again you still "appending" data to the same configuration attribute.

Solution:
 - Always override the data

Sample:

```
this.p = {'postData': {'arguments': {'filter': {'username': 'john' }}}};
```

If you call the method, you should have:

```
this.p = {'postData': {'arguments': {'filter': {'lastname': 'maria' }}}};
```

This way, the user will be free to use wherever filter he want's... if he want's first and last name, just need to set a filter with both data.

```
this.p = {'postData': {'arguments': {'filter': {'username': 'john', 'lastname': 'maria' }}}};
```