Sync clean all

[mlw]

***IMPORTANT: This PR introduces a change in behavior!***

Currently, clean syncs result in the entire rules database being deleted and newly received rules being written. However this means that any transitive rules are also wiped out, causing pain for users.

This PR changes the meaning of clean syncs to instead only delete non-transitive rules before writing the newly received rules.

The following describes the new behavior:

1. santactl sync --clean will only remove non-transitive rules
2. santactl sync --clean-all is a new flag that will remove all rules (like --clean before this PR)
3. The preflight response key clean_sync is now deprecated
4. The preflight response key clean_sync is treated as only removing non-transitive rules
5. A new preflight response key is supported, sync_type
6. The sync_type preflight response key supports the following values
   • normal - Only new rules will be added, existing rules will not be removed
   • clean - Remove non-transitive rules before writing new rules
   • clean_all - Remove all rules before writing new rules
   • Not set - Same as normal
7. The server can still force a clean or clean_all action in the preflight response
8. The client can force a clean_all action even if the server only responded with clean
   • This is because from the server's perspective, this is the same operation. A user is allowed to dictate if all rules or only transitive rules should be removed (presuming the server doesn't force all rules)

Fixes #1272

[pmarkowsky]

LGTM.