Add paging for manage user page

https://bugzilla.redhat.com/show_bug.cgi?id=1107882
You can factor-up the beginning of the query. Like:
```java
String queryString = "select count(*) from HAccount";
if (!StringUtils.isEmpty(filter)) {
    queryString +=
                  " where lower(username) like :filter";
}
```
Probably better with a StringBuilder, but you get the idea.