Fix for listUserWords

:Release Notes:
1. "listUserWords" now accept only integer as input for offset and limit
2. its returning False for all invalid offset and limit values (strings and special characters).

:Detailed Notes:
1. "listUserWords" now accept only integer as input for offset and limit
2. its returning False for all invalid offset and limit values (strings and special characters).

:Testing Performed:
Was tested on Starfish build 236.

:QA Notes:
correct request:
luna-send -n 1 -f palm://com.palm.smartKey/listUserWords '{ "offset":"0", "limit":"10"}'
wrong request:
luna-send -n 1 -f palm://com.palm.smartKey/listUserWords '{ "offset":"invalid", "limit":"$%^"}

:Issues Addressed:
[GF-10663] com.palm.smartKey:listUserWords - returns True for invalid offset and limit

Open-webOS-DCO-1.0-Signed-off-by: Igor Kuksyuk <ikuksyuk@luxoft.com>

Change-Id: I3b75b3f88fe1c718d937eeb718e9acc7c65310e2
Reviewed-on: https://g2g.palm.com/2933
Reviewed-by: Build Verification
Reviewed-by: Igor Kuksyuk <ikuksyuk@luxoft.com>
Tested-by: Igor Kuksyuk <ikuksyuk@luxoft.com>
Reviewed-by: Roger Stringer <roger.stringer@lge.com>