ui: load source from directory via MenuBar

Added MenuBar action Project->New, which opens a directory dialog for choosing the new source directory to parse the
files from. The ConfigManager can be created empty now and setValue calls can be used to set values.

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src/lib/Project.h

@@ -16,6 +16,10 @@ public:
 	~Project();
 
 	bool loadProjectSettings(const std::string& projectSettingsFile);
+	void clearProjectSettings();
+
+	bool setSourceDirectoryPath(const std::string& sourceDirectoryPath);
+
 	void parseCode();
 
 private: