Add support of disableGetFeatureInfo parameter in plugin GetFeature

With this PR it is possible to replace WMS GetFeatureInfo requests by WFS GetFeature requests when making a point query (the rectangle query being still handled by WFS GetFeature).
```
{
    ptype: "cgxp_getfeature",
    disableGetFeatureInfo: true,
    ...
}
```

Default value for "disableGetFeatureInfo" is "false", which means that the default behaviour is unchanged (GFI remains used).