Add events for initial configuration

[rmeissner]

To be able to properly track the internal state of the Safe we should emit an event for the initial configuration

[Uxio0]

Ideas:

• ExecutionSuccess could have the nonce of the executed transaction. This would be very useful
• Emit event of AddedOwner and ChangedThreshold when Safe is created

[rmeissner]

Ideas:

• Add more information to exection events: e.g. first 4 bytes, data hash, value, to