CHOP-955: Include app_settings/settings_install.xml in file_list.

viewer_manifest.py uses its base-class llmanifest.LLManifest.put_in_file()
method to create several different files in the install image being
marshalled. I based the logic to create settings_install.xml on that example.
Unfortunately I failed to notice that after every existing call, the script
also explicitly appended the newly-created file to self.file_list... which
only matters on Windows. file_list is fed to the NSIS installer.
Change put_in_file() method to implicitly append to self.file_list.
Change every existing viewer_manifest.py call to pass new put_in_file(src=)
param instead of explicitly appending to self.file_list.