Merge branch 'next'

Merge branch 'next'

This merges the next branch accumulated during the 2017.11 release
cycle back into the master branch.

A few conflicts had to be resolved:

 - In the DEVELOPERS file, because Fabrice Fontaine was added as a
   developer for libupnp in master, and for libupnp18 in
   next. Resolution is simple: add him for both.

 - linux/Config.in, because we updated the 4.13.x release used by
   default in master, while we moved to 4.14 in next. Resolution: use
   4.14.

 - package/libupnp/libupnp.hash: a hash for the license file was added
   in master, while the package was bumped into next. Resolution: keep
   the hash for the license file, and keep the hash for the newest
   version of libupnp.

 - package/linux-headers/Config.in.host: default version of the kernel
   headers for 4.13 was bumped to the latest 4.13.x in master, but was
   changed to 4.14 in next. Resolution: use 4.14.

 - package/samba4/: samba was bumped to 4.6.11 in master for security
   reasons, but was bumped to 4.7.3 in next. Resolution: keep 4.7.3.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>