Ensure that a base language is loaded before custom theme

Main goal of this patch is to improve error handling when a custom
theme does not contain a valid theme version. We were getting a
message saying that the theme_ver_err resource did not exist as
well as an error saying that the package had failed to load. Now
we properly get a single error message about the theme version.

Change-Id: I361ef2d139220bbeaf2e856be919dc3a50ae4299
diff --git a/gui/pages.hpp b/gui/pages.hpp
index 87e1fb5..b2f2580 100644
--- a/gui/pages.hpp
+++ b/gui/pages.hpp
@@ -91,7 +91,7 @@
 
 public:
 	int LoadLanguage(char* languageFile, ZipArchive* package);
-	int Load(ZipArchive* package, char* xmlFile, char* languageFile);
+	int Load(ZipArchive* package, char* xmlFile, char* languageFile, char* baseLanguageFile);
 	int CheckInclude(ZipArchive* package, xml_document<> *parentDoc);
 
 	Page* FindPage(std::string name);