Index essential addresses when emitting events

[mmv08]

Context/issue

Per suggestion from the safe forum, https://forum.gnosis-safe.io/t/safe-contract-v1-4-0/2109/20, it's tricky to index module changes off-chain.

Proposed solution

Take the suggestion and widen the scope a little bit, and index all essential addresses in the safe contract:

• owner additions and removals
• fallback manager changes
• module additions and removals
• transaction guard changes

Alternatives

• Do nothing

Additional context