feat: support custom shortcut for existing actions

Resolve https://github.com/BLumia/pineapple-pictures/issues/128

Actually also https://github.com/BLumia/pineapple-pictures/issues/72
but not sure why that one is now a 404 page.

CMakeLists.txt

@@ -66,6 +66,7 @@ set (PPIC_CPP_FILES
     app/metadatadialog.cpp
     app/exiv2wrapper.cpp
     app/playlistmanager.cpp
+    app/shortcutedit.cpp
 )
 
 set (PPIC_HEADER_FILES
@@ -85,6 +86,7 @@ set (PPIC_HEADER_FILES
     app/metadatadialog.h
     app/exiv2wrapper.h
     app/playlistmanager.h
+    app/shortcutedit.h
 )
 
 set (PPIC_QRC_FILES