Support import of scripture portions

[eb1]

Currently, AIM supports the import of whole scripture books, or chapter-wise import (so long as the first chapter is imported first). This works most of the time. However, there is a use case for importing scripture portions -- the "Ramp" approach to OT scripture portions outlined by Hanni Kuhn (outlined here).

In order to support scripture portion import, AIM will need to do the following:

1. Be able to identify a document as a "scripture portion" rather than a full text.
2. Input from the user any missing information about the scripture portion -- book name, chapter numbers (if missing), etc.
3. In the case where the user needs to go back and do a full translation of a portion, successfully import and merge a full text such that the existing translated portions are not lost.

Items 1 and 2 should be considered in this issue; I'll write up a separate issue for merging a full document into a project that already has portions of the same book / chapter.