Introduction of RPL non-storing mode

This is the first commit for discussion. It works - but e.g. the checksum in UDP-packages is wrong because the length is zero (which it is not btw). In addition the design decisions concerning messages sending/relaying may be discuss-able - but I think they are as noninvasive as the network stack would allow them to be.

At last - the proposed fixes concerning storing/non-storing mode files with the same declaration-base in one directory from @Kijewski does not work. (Both - excluding files or moving them to a sub-directory) But I will see more into it. Maybe someone can help.
Right. For example the UDP destination is something like ABCD::#ID and all stored routing addresses are 1234::#ID, the root needs to check if there is a way to the destination. It can then of course not compare the whole address, just the host suffix. Since the nature of having different IPv6-addresses in the current structure of RPL this I think is the only way handling it. Or do you have any suggestions?