Support simple filter, like only scan row key.

Example:

Java code:

```java
FilterList filterList = new FilterList(FilterList.Operator.MUST_PASS_ALL);
filterList.addFilter(new FirstKeyOnlyFilter());
filterList.addFilter(new KeyOnlyFilter());
Scan scan = new Scan(Bytes.toBytes("scanner-row0"));
scan.setFilter(filterList);
```

Nodejs code:

```js
var filterList = new filters.FilterList(filters.FilterList.Operator.MUST_PASS_ALL);
filterList.addFilter(new filters.FirstKeyOnlyFilter());
filterList.addFilter(new filters.KeyOnlyFilter());
var scan = new Scan('scanner-row0');
scan.setFilter(filterList);
```
add missing filter name
Merge pull request #53 from alibaba/simple-filter

Support simple filter, like only scan row key.