A few renames in OFArray, OFDataArray and OFDictionary.

OFArray:
 * Rename - object: to - objectAtIndex:.

OFDataArray:
 * Rename - item: to - itemAtIndex:.

OFDictionary:
 * Rename - get: to - objectForKey:.
 * Rename - set:to: to - setObject:forKey:.
 * Rename - remove: to - removeObjectForKey:.