v0.73.0 Adding Encryption

Major Changes

• RealmConfiguration.EncryptionKey added so files can be encrypted and existing encrypted files from other Realm sources opened (assuming you have the key).

Minor Fixes

• For PCL users, if you use RealmConfiguration.DefaultConfiguration without having linked a platform-specific dll, you will now get the warning message with a PlatformNotSupportedException. Previously threw a TypeInitExepction.
• Update to Core v0.96.2 and matching ObjectStore (issue #393)