Merge pull request #92 from NicolaAccettura/develop_FW-262

FW-262. OpenMoteCC2538 leds.
FW-252. First version of OTF (i.e. no retries).
FW-252. Fixing build.
Merge pull request #93 from openwsn-berkeley/develop_FW-252

FW-252. Fix.
Merge branch 'develop' of https://github.com/openwsn-berkeley/openwsn-fw into develop