[navi_toolkit] OdometryHelper checks / info if odom is available

[AlexReimann]

Fix for issue #110:

• Add bool return for getting stuff
• Initialized() function to check if initialized

[stonier]

Exceptions not preferable?

[stonier]

It'll do...exceptions would be nicer, but if you use this in a fast loop, then the usual convention of int error codes would be preferable. The other thing would be to just check if it's initialised. Not like it ever gets uninitialised. Then you could leave them as void functions.