Degenerate slugs

Fixes #2671, tweaks contentload to be more meaningful.

Summary of changes:
* Prevent periods in file names causing slug collisions
* Check for slug collisions for already generated slugs
* Give verbose output for assessment items and contents put in topic tree.
Oh, I was confused on how this is being used. So it's a set of all slugs, but is it being used somewhere else before getting delete?