Track-and-trace dapp improvements

[DOBEN]

Task description
Summary of improvements for the track-and-trace dapp:

Sub-tasks

• Display version at the front end.
• Add link at front-end to the source code repo.
• Generalize the state machine so that we can easily add/remove new addresses to be producer/seller/... via the front end.
• Enable updating of the account when switching an account in the wallets
• Improve error messages shown in the admin pages on the front end.
  - For example when a non-admin tries to add itself as admin:
  
• Make navbar not transparent to avoid overlap in text
  
• Create a migration script that allows us to read out the current state-machine and admins as set in the smart contract and initialize a new smart contract instance with the same state. This enables us to easily roll out new versions of the hosted dapp without manually adding admins to a newly deployed contract.