Update help text for contentdm

refs #5232

Update example text for Contentdm help page, and update the sample
contentdm-related replacementDics, which show up as the default data on the
contentdm config page.
Cleanup around AtoM upload settings

refs #5232

Misc cleanup around AtoM and other DIP upload settings: removed unused
functions & templates, renamed AtoM settings template to match other dip
upload settings.  Updated the AtoM settings to use a modelform.