Links (#615)

* add URL support to Label element and XML parsing

* refactor Label URL handling to use getter method in setURL

* implement URL opening confirmation dialog and platform-specific URL handling

* fix: fixed build errors

* remove: delete test link label from worlds.xml

* refactor: remove URL handling from Label class and XML parsing

* refactor: clean up Label class by removing unnecessary whitespace and improving code readability

* refactor: remove unused URL member from Label class

* refactor: remove unused URL attribute from XML UI documentation and related code

* refactor: improve code readability by adding whitespace and formatting adjustments in Label class

* refactor: improve whitespace consistency in Label class and add URL opening functionality in libcore

src/util/platform.hpp

@@ -13,4 +13,5 @@ namespace platform {
     /// Makes the current thread sleep for the specified amount of milliseconds.
     void sleep(size_t millis);
     int get_process_id();
+    bool openURL(const std::string& url);
 }