Improving the curate generator

Working towards making the `rails g curate` more replayable:

* by gracefully skipping migration duplicates (or allowing -f to
  obliterate)
* by passing any -f parameters to sufia:models:install

Also tidying up a bit of loose behavior regarding route injection and
devise.

Related to ndlib/planning#91
Merge pull request #92 from ndlib/improving-curate-generator

Improving the curate generator