feat: Save opened projects as recent entries (#1105)

This PR does two things :
- save opened projects as recent entries
- refactor stuff about recent entries in a separate file. The reason is
that I felt like welcome_screen.cpp was really big ( 685 lines before
this, 500 now). What do you think ?

---------

Co-authored-by: Nik <werwolv98@gmail.com>

lib/libimhex/source/api/project_file_manager.cpp

@@ -86,6 +86,7 @@ namespace hex {
         }
 
         resetPath.release();
+        EventManager::post<EventProjectOpened>();
         EventManager::post<RequestUpdateWindowTitle>();
 
         return true;