Make CSP vote flow more similar to the anonymous flow

[elboletaire]

Right now the CSP voting flow shows a "Vote" button that actually opens a popup to login to the CSP provider. This is confusing and causes a big issue: you can't actually check your vote with this current flow.

I propose changing it to follow the same flow we use in the anonymous votings, but slightly changing the translation. So instead of "Sign first" I'd say "Sign in first", since you have to sign-in via an external provider.