tests: let license checker check headers, too
core: introduce KERNEL_PID_FIRST and KERNEL_PID_LAST
core: let valid PIDs start with 1
unittests: do not use auto_init
core: clist is a cyclic list
core: clist without explicit thread

Right now the core component `clist` is a generic cyclic doubly-linked list.
In the core it is used in `tcb_t::rq_entry`.
Further it is used `net_if.c`.

This commit removes the member `clist_node_t::data` which stored the
pointer to the `tcb_t` instance of which the clist is already a member.
The needless member added `sizeof (int)` bytes to every instance of
`tcb_t`.

In `net_if.c` the clist was used in a type-punned way, so that the
change won't affect it.
examples: renamed rpl_udp header
examples: cleanup for rpl_udp

* removed unnecessary shell commands
* updated documentation
* Unified global default IP address
rpl: moved headers to sys/net/include
examples: don't advertise IPv6 prefix

Cleaning up the IPv6 address initialization and removed the addition of
an IPv6 prefix to advertise.
examples: use correct broadcast address when sending
fix low-level sending destination address
Merge pull request #1531 from LudwigOrtmann/header_license_headers

tests: let license checker check headers, too
Merge pull request #1013 from Kijewski/clist_wo_thread

 core: clist without explicit thread
tests: Fix tests that were defect

* I used pexpect instead of when expect script was not working expect, since
  TCL confuses me
* I deleted the thread_exit test since it was completely invalid
Merge pull request #1596 from authmillenon/fix-expect

tests: Fix tests that were defect
Merge pull request #1594 from authmillenon/unittests-no-auto-init

unittests: do not use auto_init
licenses: updated some missing licenses in headers
boards:make: hardcode goodfet.bsl path in Makefile.include
goodfet: hardcode python version to 2.7