Move showTooManyFilesWarning to the wizard object

This was stupid and it made refactoring the upload stuff very difficult

Also moved the handler construction out of the Upload constructor, because
we don't need it until later.

Bonus: Tore out uploadToAdd, which is stupid anyway.

Change-Id: I5357cc9e5bc40528d6f30fd92a5f798194e37b48
Merge "Move showTooManyFilesWarning to the wizard object"