Update to custom AWSSDK package (BL-497)

This nuget package was build with a patch that fixes the
downloading on Linux (https://github.com/ermshiperete/aws-sdk-net).
Fix longpress for Decodable/Leveled Reader (BL-620)

Need to use JohnT's offset method of resetting the cursor
rather than just saving the range as before.

This moves three methods from ReaderToolsModel
to the new EditableDivUtils.
Merge pull request #111 from ermshiperete/BL-497

Update to custom AWSSDK package (BL-497)
Fix new book thumbnails on Linux (BL-505)
Merge pull request #106 from andrew-polk/BL620_DRLongPressFix

Fix longpress for Decodable/Leveled Reader (BL-620)
Merge pull request #110 from andrew-polk/BL505_LinuxNewBookThumb

Fix new book thumbnails on Linux (BL-505)