refactor: move file open event handling to standalone file

CMakeLists.txt

@@ -68,6 +68,7 @@ set (PPIC_CPP_FILES
     app/exiv2wrapper.cpp
     app/playlistmanager.cpp
     app/shortcutedit.cpp
+    app/fileopeneventhandler.cpp
 )
 
 set (PPIC_HEADER_FILES
@@ -88,6 +89,7 @@ set (PPIC_HEADER_FILES
     app/exiv2wrapper.h
     app/playlistmanager.h
     app/shortcutedit.h
+    app/fileopeneventhandler.h
 )
 
 set (PPIC_QRC_FILES