Add Organizational event logging feature

This PR adds event/audit logging support for organizations.
By default this feature is disabled, since it does log a lot and adds
extra database transactions.

All events are touched except a few, since we do not support those
features (yet), like SSO for example.

This feature is tested with multiple clients and all database types.

Fixes #229

src/db/models/mod.rs

@@ -3,6 +3,7 @@ mod cipher;
 mod collection;
 mod device;
 mod emergency_access;
+mod event;
 mod favorite;
 mod folder;
 mod group;
@@ -18,6 +19,7 @@ pub use self::cipher::Cipher;
 pub use self::collection::{Collection, CollectionCipher, CollectionUser};
 pub use self::device::Device;
 pub use self::emergency_access::{EmergencyAccess, EmergencyAccessStatus, EmergencyAccessType};
+pub use self::event::{Event, EventType};
 pub use self::favorite::Favorite;
 pub use self::folder::{Folder, FolderCipher};
 pub use self::group::{CollectionGroup, Group, GroupUser};