Some commenting fixes in Backup.

Conflicts:
	app/models/backup.rb
Some commenting fixes in Backup.

Conflicts:
	app/models/backup.rb
Refactor Backup#dump into multiple methods.
Refactor Backup#import into multiple methods.

Conflicts:
	app/models/backup.rb
Better class docs for Backup model.
Rename Backup#import to #restore.

Conflicts:
	app/models/backup.rb
Restructure Backup.
Drop Tenant#export.
Refactor Backup method so it has also a class method interface for command line.
Add UPGRADE.textile.