(io): make igtlProtocol::MessageFactory extendable from other libraries
Description
Make the MessageFactory public, to be used from outside of igtlProtocol
.
This is helpful to registrar new type of IGTL Messages that are not necessary implemented in igtlProtocol
library.
Closes #631 (closed)
How to test it?
Try to access the MessageFactory from an other library, or a main.
Test your favorite app using igtl.