Add installer-purple variant

build.sh:

Note that the installer-purple variant does NOT include the offline
profile, that's on purpose. There's no requirement for this installer to
work offline, and on top of that, we can't include all the packages in
the iso at the moment (the package exploitdb-papers is too big). So we
very much expect to have network, and to download big packages during
the installation.

See next commits for more details.

    kali-config/installer-purple/packages:

Unlike other variants, the "base" metapackage is kali-system-core,
which is a very stripped down metapackage with no offensive tools.
(kali-system-core is basically what used to be kali-linux-core, minus
the few offensive tools that were in there).

build.sh

@@ -325,6 +325,10 @@ case "$IMAGE_TYPE" in
 			export DISKTYPE="NETINST"
 			profiles="kali"
 			auto_profiles="kali"
+		elif [ "$KALI_VARIANT" = "purple" ]; then
+			export DISKTYPE="BD"
+			profiles="kali kali-purple"
+			auto_profiles="kali kali-purple"
 		else    # plain installer
 			export DISKTYPE="BD"
 			profiles="kali offline"

kali-config/installer-purple/packages

@@ -0,0 +1,19 @@
+# Installer for Kali Purple
+
+# Metapackages
+# You can customize the set of Kali metapackages (groups of tools) available
+# in the installer ISO.
+# For the complete list see: https://tools.kali.org/kali-metapackages
+kali-system-core
+
+# Tools
+kali-tools-detect
+kali-tools-identify
+kali-tools-protect
+kali-tools-recover
+kali-tools-respond
+
+# Graphical desktops
+kali-desktop-xfce
+kali-desktop-gnome
+kali-desktop-kde