make: dedup USEMODULE_INCLUDES w/o shelling out

Currently, `USEMODULE_INCLUDES` is deduplicated using a combination of
`tr` and `awk`. The proposed method achieves a deduplication (no
sorting) without the need to shell out by using make internals only.

kinetis: Conditionally enable MCG

cpu/stm32f4: add support for stm32f405rg

gnrc_netif: Enable RX and TX complete events after netdev init

Signed-off-by: Gilles DOFFE <gilles.doffe@savoirfairelinux.com>

sock: Add dependencies for sock_util

github: move ISSUE_TEMPLATE.md to ISSUE_TEMPLATE/bug_report.md

cpu/stm32l4: add adc implementation

pseudomodules: allow defining them in pkg/PKG/Makefile.include

Officially allow packages to define pseudomodules in their Makefile.include as
done in the libcose package.

net: add Asymcute, an asynchronous MQTT-SN client implementation

GitHub supports different types of issue templates for a while now.
The following types are supported:

* Bug report
  (living in `.github/ISSUE_TEMPLATE/bug_report.md`),
* Feature request
  (living in `.github/ISSUE_TEMPLATE/feature_request.md`), and
* Custom issue template
  (living in `.github/ISSUE_TEMPLATE/custom.md`)

Our current issue template is mostly a bug report template, so this
moves it to `.github/ISSUE_TEMPLATE/bug_report.md`.

Makefile.include: fully define BASELIBS before using its value

mosquitto_rsmb: add MQTT listener to config

This helped me a lot while testing #9464 to interact with the broker
using the mosquitto shell command clients.

gnrc_ipv6_nib: Add capability to handle and send RDNSS option

sock_util: add posix dependency

core/byteorder: fix naming for htobebufs/bebuftohs functions

`sock_util` includes the `arpa/inet.h` header so it has `posix` as a
dependency to include the `sys/posix/include` include path.

drivers/at: at out-of-band data support for at commands parser

tests: cpu_efm32_features: add test application

Add SRAM based PRNG seeder