Add opl-secret-ballot

[aefhm]

Why

Add example code to support documentation and tutorials.

[matevz]

Seems fine for the initial migratiom. I'll test it tomorrow and let you know if I run into any issues.

The only thing that bothers me is whether the folder should be called secret-ballot-opl instead - If we make another non-opl version of the ballot. This would need a change in all package.json files though (eg. @oasislabs/secret-ballot-opl-frontend).

[aefhm]

Seems fine for the initial migratiom. I'll test it tomorrow and let you know if I run into any issues.

The only thing that bothers me is whether the folder should be called secret-ballot-opl instead - If we make another non-opl version of the ballot. This would need a change in all package.json files though (eg. @oasislabs/secret-ballot-opl-frontend).

Hmm. I think it is okay to make that change in the future or that resetting a tutorial is reasonable.