Add three catalog setups, for UK mirror

The fgaddon-catalog was duplicated to avoid disturbing Curt’s config
he runs locally, until the new setup is working.

catalog/stable-2018-catalog/template.xml

@@ -0,0 +1,33 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--Template catalog - copy and modify for your site as required-->
+<PropertyList>
+  <template>
+    <version n="0">2018.*.*</version>
+    <id>org.flightgear.fgaddon.stable_2018</id>
+    <license>GPL</license>
+    <url>http://mirrors.ibiblio.org/flightgear/ftp/Aircraft-2018/catalog.xml</url>
+    <name>FlightGear aircraft distribution for 2108.x versions</name>
+    <description>This hangar provides aircraft officially supported and maintained 
+    by the FlightGear project, under a free-software license. These aircraft
+    are compatible with FlightGear versions from 2018.</description>
+    
+    <alternate-version>
+      <version>2019.*</version>
+      <url>http://mirrors.ibiblio.org/flightgear/ftp/Aircraft/catalog.xml</url>
+      <id>org.flightgear.fgaddon</id>
+    </alternate-version>
+
+    <alternate-version>
+      <version>2017.*</version>
+      <url>http://mirrors.ibiblio.org/flightgear/ftp/Aircraft-legacy/catalog.xml</url>
+      <id>org.flightgear.fgaddon.legacy</id>
+    </alternate-version>
+
+    <!-- alternate version previously did not allow multiple version entries, so we
+    duplicate the alternate version here -->
+    <alternate-version>
+      <version>2016.*</version>
+      <url>http://mirrors.ibiblio.org/flightgear/ftp/Aircraft-legacy/catalog.xml</url>
+      <id>org.flightgear.fgaddon.legacy</id>
+    </alternate-version>
+</PropertyList>