Debian packaging improvements

- Build binary on "any" architecture
- Binary depends on adduser
- Improve postinst script

Signed-off-by: Tormod Volden <debian.tormod@gmail.com>

distributions/debian/control

@@ -17,10 +17,11 @@ Vcs-Git: git://github.com/corrados/jamulus.git
 Vcs-Browser: https://github.com/corrados/jamulus
 
 Package: jamulus
-Architecture: i386 amd64 armhf
+Architecture: any
 Depends:
  ${shlibs:Depends},
  ${misc:Depends},
+ adduser,
  jackd,
  qt5-default,
  qtchooser,

distributions/debian/postinst

@@ -1,2 +1,9 @@
-#!/bin/bash
-adduser --system jamulus
+#!/bin/sh
+
+set -e
+
+# dh_sysuser can be used in newer distro releases
+
+adduser --system --quiet jamulus
+
+#DEBHELPER#