[1.7.x] Fixed documentation of GeoModelAdmin.openlayers_url

Backport of e3091350 from master.
[1.7.x] Fixed typo in docs/ref/applications.txt.

Backport of 0fde2ca0368928bb8ee16b06b8ca33031bb779b7 from master
[1.7.x] Cleaned up a note in docs/topics/db/sql.txt.

Backport of 34a06d99e0fc96a0f0648bfde141d342e963e971 from master
[1.7.x] Fixed #23965 -- Mentioned that FieldFile inherits from File

Backport of 5281d9620d13386fd4403f7aa6b9a2afd9b5a93f from master