When selecting multiple mods at once, it can become hard to keep track
of which ones you selected.
To address this, a dialog is now displayed
when you finish selecting the mods to download, showing you which ones
you selected and their filenames. From there, you can either accept it
and download the mods, or you can cancel it and go back to the mod
selection dialog.
Previously, we used a unique_ptr to a ModDownloadTask to keep track of
the selected mod to download when we accepted the dialog.
In order to allow multiple mods to be selected at once for download,
this has been changed to a QHash where the key is the mods name (since
it doesn't seem right to allow for multiple versions of the same mod to
be downloaded at once), and the value is a pointer to the corresponding
ModDownloadTask.
