Introduce FileViewManager::AddOrEditSystemApp
Dont forget to update the internal systemApps
OpenWithDialog now itself adds the programs to systemApps
FileViewManager saving bugfix
AppListItemDelegate drawing bugfix
Handle (de)selecting the apps in OpenWithDlg
prevent re-adding already existent programs
app list alternating colors are now done correctly

We use our custom index instead of row number now, which works correctly
even when we hide items.