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/include/hex/api/event.hpp

@@ -195,6 +195,11 @@ namespace hex {
     EVENT_DEF(EventStoreContentRemoved, const std::fs::path&);
     EVENT_DEF(EventImHexClosing);
 
+    /**
+     * @brief Called when a project has been loaded
+     */
+    EVENT_DEF(EventProjectOpened);
+
     EVENT_DEF_NO_LOG(EventFrameBegin);
     EVENT_DEF_NO_LOG(EventFrameEnd);
     EVENT_DEF_NO_LOG(EventSetTaskBarIconState, u32, u32, u32);