Use /twres instead of /res for theme resources

AOSP and other ROM trees now do a rm -rf of the res folder during
the ramdisk creation process that removes the TWRP resources.
Using /twres instead of /res works around this issue making TWRP
more compatible with AOSP and other build trees.

Change-Id: I0d4c7e06ca381ac5aa0069b6f2b8c47f7dec49e7

gui/resources.cpp

@@ -100,7 +100,7 @@ FontResource::FontResource(xml_node<>* node, ZipArchive* pZip)
 		}
 		else
 		{
-			file = std::string("/res/fonts/") + file;
+			file = std::string(TWRES "fonts/") + file;
 			mFont = gr_ttf_loadFont(file.c_str(), size, dpi);
 		}
 	}