GEOMESA-311 Handle 'attr1 and attr2' filters

If multiple attribute filters are indexable, use the first one
In the future, a query optimizer will make more informed decision
This might be quicker with using this function (https://github.com/locationtech/geomesa/blob/accumulo1.5.x/1.x/geomesa-core/src/main/scala/org/locationtech/geomesa/core/filter/package.scala#L100-109)
```
if (spatialFilter(filter) && isValidSTIdxFilter(......)) Some(new STIdxStrategy) else None
```