Calculate checksums for imported images

The checksum algorithm has been changed from SHA-1 to Adler32
(with the possibility of further extension). The new faster algo
calculates values, that are then stored in the Pixels table.
Changes have been implemented both client- and server-side.
Add missing reset() call
Add Google Guava 13.0 (JDK 1.5)
Update model with checksumValue and checksumType

This commit should serve as a template to look at when implementing
model changes related to OriginalFile and Pixels. It renames sha1
to checksumValue and adds an optional checksumType column.
Future commits should add setting the checksum type appropriately
in all (and maybe more) file that have been changed here.
TMP: Ongoing checksum changes