Replace shell script with Rakefile
Add gem lockfile
Update gitignore
Remove git from plain
Adjust readme
Use US debian mirror
Don't use LVM
Streamline preseeds
Move git installation to preseed
Revert "Move git installation to preseed"

This reverts commit ec080e080cb46f2d8ac18df16c1c996c9fd82a5b.
Combine default/plain assets
Remove git provisioner from plain
Adjust upload task
Formatting
Read template JSON to get box filename