E2e fixes

[ineiti]

This PR does the following:

• Comments and error handling
• Improve speed of docker build
• Add voting script to the backend
• Putting FormFromStore into a single place
• Correctly store and retrieve DKGs
• Synching of nonces is now done in dela
• Making tests pass

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[PascalinDe]

isn't that a different DELA repository now?

[ineiti]

go does some magic here:

$ go list -f '{{.Dir}}' go.dedis.ch/dela
.../packages/pkg/mod/github.com/c4dt/[email protected]

and because we kept the go.dedis.ch/dela as package name throughout the github.com/c4dt/d-voting, and rely on the replace directive in go.mod, I think it's OK.

Change my mind :)