rtt_rosparam: Support more primitive integral parameter

[Hugal31]

Add support for more primitive parameters in rtt_rosparam.

Currently, we only support those primitive integral types:

• int
• unsigned int
• char
• unsigned char

(See code fox xml -> prop and prop -> xml).

Other integral types, such as longs and shorts are missing. It would be nice to support them, and maybe add an error/warning if the value doesn't fit into the prop/xml value (this is already missing for currently supported integrals).