footnotes_views: Fix the teaser field

[olafgrabienski]

Mentioned by @docwilmot in #9:

the Views submodule for now only provides a full view mode field

[olafgrabienski]

I've had a look at the Views integration and can confirm the issue. Actually, the submodule provides a "body" and a "teaser" field for footnotes, but both of them display the same full view mode.

[olafgrabienski]

Removing the "release blocker" tag, hoping that people who need the display of Teaser text and corresponding footnotes in Views will help to fix the issue.