Blocks are now saved to and restored from course backups!

Blocks are now saved to and restored from course backups!

Backward compatibility is maintained, i.e. you can restore ANY version
backups without problems in 1.5. When "adding backup data to an existing
course", no blocks are added. I 'm not sure what the correct behavior
would be in this case.

When restoring a backup from Moodle <= 1.2, the new course SHOULD be given
default blocks when it is restored. I have not actually tested this, my
tests were with version 1.3 and 1.4 backup format.