GEOMESA-136 WPS processes for Geomesa Query and Geomesa Proximity Search

What about error-handling?  Should we use the safety-scissors approach as in

```scala
// ...
def poly = sf.getDefaultGeometry match {
  case p: Polygon => Option(p)
  case _                => None
}
// ...
```

or should we simply assume that the user is responsible for trapping any errors that arise when asking for the wrong sort of geometry?