branding: Add a shortProductName entry.

This is what the bootloader modules really want, and it was also missing
for consistency with the other branding entries.

src/branding/default/branding.desc

@@ -3,6 +3,7 @@ componentName:  default
 
 strings:
     productName:        Generic GNU/Linux
+    shortProductName:   Generic
     version:            1.0 LTS
     shortVersion:       1.0
     versionedName:      Generic GNU/Linux 1.0 LTS "Rusty Trombone"

src/libcalamaresui/Branding.cpp

@@ -50,7 +50,8 @@ QStringList Branding::s_stringEntryStrings =
     "version",
     "shortVersion",
     "versionedName",
-    "shortVersionedName"
+    "shortVersionedName",
+    "shortProductName"
 };
 
 
@@ -206,11 +207,8 @@ void
 Branding::setGlobals( GlobalStorage* globalStorage ) const
 {
     QVariantMap brandingMap;
-    brandingMap.insert( "productName", string( ProductName ) );
-    brandingMap.insert( "version", string( Version ) );
-    brandingMap.insert( "shortVersion", string( ShortVersion ) );
-    brandingMap.insert( "versionedName", string( VersionedName ) );
-    brandingMap.insert( "shortVersionedName", string( ShortVersionedName ) );
+    foreach ( const QString& key, s_stringEntryStrings )
+        brandingMap.insert( key, m_strings.value( key ) );
     globalStorage->insert( "branding", brandingMap );
 }
 

src/libcalamaresui/Branding.h

@@ -42,7 +42,8 @@ public:
         Version,
         ShortVersion,
         VersionedName,
-        ShortVersionedName
+        ShortVersionedName,
+        ShortProductName
     };
 
     enum ImageEntry : short