themeeditor: Fix dmg deploy steps.

- Fix binary name in Info.plist.
- Run dmgbuild as Python module, in some cases it isn't available directly.
- Add missing dmgbuild configuration for themeeditor.

Change-Id: I2db50959b88283f43e2203cf71b130cdb33103dd

utils/themeeditor/Info.plist

@@ -3,7 +3,7 @@
 <plist version="0.9">
     <dict>
         <key>CFBundleExecutable</key>
-        <string>rbthemeeditor</string>
+        <string>RockboxThemeEditor</string>
         <key>CFBundleName</key>
         <string>Theme Editor</string>
         <key>CFBundleShortVersionString</key>

utils/themeeditor/dmgbuild.cfg

@@ -0,0 +1,17 @@
+# Configuration for creating a dmg with dmgbuild
+# (https://github.com/al45tair/dmgbuild)
+# Requires at least Python 3.4
+
+import os
+import plistlib
+
+_appbundle = defines['appbundle']
+_plfile = open(os.path.join(_appbundle, 'Contents/Info.plist'))
+_pldata = _plfile.read().encode()
+_plist = plistlib.loads(_pldata)
+_iconfile = os.path.join(_appbundle, 'Contents/Resources', _plist['CFBundleIconFile'])
+
+files = [ _appbundle ]
+icon = _iconfile
+background = '#c6d6f5'
+