Use DotBot-libs?

[geonnave]

To enable integration of Mari into applications of the DotBot-firmware repo, me and @aabadie have discussed a refactoring where Mari uses the drivers from DotBot-libs instead.

The benefits of doing this are:

• allow Mari to also be used in "normal" DotBot firmware (without SwarmIT)
• reduce code duplication

On the other hand, this requires backporting some changes done to Mari's radio driver, back to the corresponding radio driver in DotBot-libs (and possibly also to other drivers, such as timer and rng).

Finally, I am not sure how that would work with SwarmIT, since right now:

SwarmIT -> DotBot-libs
        -> Mari

(where -> means "depends on")

... and if we do this refactor, then:

SwarmIT -> DotBot-libs
        -> Mari -> DotBot-libs