gui: support string resources

storing strings in a map (for fast lookup) in resource manager

To define a string resource in <resources>:
<string name="foo">Hello</string>

To use a string, e.g.:
<text>%@foo%</text>

Not yet done: language-specific resources (should be solved not only for
strings, but for all kinds of resources - e.g. for localized images)

Change-Id: I3ba5cf5298c09e0d28a83973e9662f179271b33f

gui/objects.hpp

@@ -217,9 +217,6 @@ protected:
 	int mFontHeight;
 	unsigned maxWidth;
 	unsigned charSkip;
-
-protected:
-	std::string parseText(void);
 };
 
 // GUIImage - Used for static image