Added some results from researching input tools.

Unity3D provides a -not so-flexible input system. In particular it does
not  allows user to define and/or rebind controls at runtime.
We have three possible solutions:
1. Stick to Unity3D control system (ok if the game has simple controls);
2. Build our own Input Manager (hard and long way to implement, but
maximum flexibility);
3. Adopt a third party tool (faster, not so flexible, could be costly or
have a license constraint).