Implement isAuthorised in the contract

[MaximeZmt]

Currently implemented in https://github.com/c4dt/d-voting/blob/main/web/backend/src/authManager.ts should be part of: https://github.com/c4dt/d-voting/blob/main/contracts/evoting/evoting.go

Steps:

• [x] #105
• [x] #106
• [x] #107
• [x] #108
• [x] #109
• [x] #110
• [x] #111