Update repository identities after all mutations to users and email addresses

Summary:
Ref T13444. Currently, many mutations to users and email addresses (particularly: user creation; and user and address destruction) do not propagate properly to repository identities.

Add hooks to all mutation workflows so repository identities get rebuilt properly when users are created, email addresses are removed, users or email addresses are destroyed, or email addresses are reassigned.

Test Plan:

• Added random email address to account, removed it.
• Added unassociated email address to account, saw identity update (and associate).
  • Removed it, saw identity update (and disassociate).
• Registered an account with an unassociated email address, saw identity update (and associate).
  • Destroyed the account, saw identity update (and disassociate).
• Added address X to account A, unverified.
  • Invited address X.
  • Clicked invite link as account B.
  • Confirmed desire to steal address.
  • Saw identity update and reassociate.

Maniphest Tasks: T13444

Differential Revision: https://secure.phabricator.com/D20914