Update outdated year references to 2015.

Use 2015 insteaf of 201x, mostly in the manual and .plist files.

interface/wx/generic/aboutdlgg.h

@@ -34,7 +34,7 @@
         aboutInfo.SetName("MyApp");
         aboutInfo.SetVersion(MY_APP_VERSION_STRING);
         aboutInfo.SetDescription(_("My wxWidgets-based application!"));
-        aboutInfo.SetCopyright("(C) 1992-2012");
+        aboutInfo.SetCopyright("(C) 1992-2015");
         aboutInfo.SetWebSite("http://myapp.org");
         aboutInfo.AddDeveloper("My Self");