tang: Add package into tree

Tang is lightweight server for binding data to network presence.
---
Tang's source: https://github.com/latchset/tang

Maintainer: @Tiboris

Compile tested: (mips, TL-WR842N, 17.01.4, r3560-79f57e422d)

**Tang requires a few other software libraries:**

1. libhttp-parser
2. xinetd's socket activation
3. jose >= 8

**Two new files compared to tang upstream:**
- tangdx : configuration file for xinetd
- tangdw : wrapper for tangd service
	- puts timestamp when service activated, and
	- redirects stderr to log file in /var/log/

**Removed systemd requirement**

Signed-off-by: Tibor Dudlák <tdudlak@redhat.com>

utils/tang/patches/rm-systemd-from-configure.patch

@@ -0,0 +1,37 @@
+diff --git a/configure.ac b/configure.ac
+index b51bb31..4b37d30 100644
+--- a/configure.ac
++++ b/configure.ac
+@@ -27,32 +27,6 @@ AC_CHECK_LIB([http_parser], [http_parser_execute],
+              [AC_MSG_ERROR([http-parser required!])])
+ 
+ PKG_CHECK_MODULES([jose], [jose >= 8])
+-PKG_CHECK_MODULES([systemd], [systemd])
+-
+-AC_ARG_WITH([systemdsystemunitdir],
+-            [AS_HELP_STRING([--with-systemdsystemunitdir=DIR], [Directory for systemd service files])],
+-            [],
+-            [with_systemdsystemunitdir=$($PKG_CONFIG --variable=systemdsystemunitdir systemd)])
+-
+-AC_SUBST([systemdsystemunitdir], [$with_systemdsystemunitdir])
+-
+-for ac_prog in systemd-socket-activate systemd-activate; do
+-    AC_CHECK_PROG([SD_ACTIVATE], [$ac_prog], [$as_dir/$ac_prog], [],
+-		  [$PATH$PATH_SEPARATOR$($PKG_CONFIG --variable=systemdutildir systemd)])
+-    test -n "$SD_ACTIVATE" && break
+-done
+-
+-test -n "$SD_ACTIVATE" || AC_MSG_ERROR([systemd-socket-activate required!])
+-
+-AC_MSG_CHECKING([systemd-socket-activate inetd flag])
+-if $SD_ACTIVATE --help | grep -q inetd; then
+-    SD_ACTIVATE="$SD_ACTIVATE --inetd"
+-    AC_MSG_RESULT([--inetd])
+-else
+-    AC_MSG_RESULT([(default)])
+-fi
+-
+-AC_SUBST(SD_ACTIVATE)
+ 
+ TANG_CFLAGS="\
+ -Wall \