ui: reworked StartScreen and ProjectSettupScreen UI flow

* realigned buttons and elements
* fixed retina styles for mac
* removed MessageLoadSource and subsequent functionality
* edit existing project through menu
* browsing paths from the line item in QtDirectoryListBox
* grow QtDirectoryListBox instead of scroll
* take any file or directory as valid path
* fixed new project setup screen background
* fixed screen handling on cancelation

src/lib/Project.h

@@ -22,8 +22,6 @@ public:
 	void clearProjectSettings();
 	void reloadProjectSettings();
 
-	bool setSourceDirectoryPath(const std::string& sourceDirectoryPath);
-
 	void clearStorage();
 	void parseCode();