do something with InvalidMacExceptions & InvalidComponentExceptions

[rhodey]

When downloading contacts and events from the remote server both InvalidMacException and InvalidComponentException may be thrown, these indicate an error in decryption and an error in vcard & ical parsing respectively.

At the time of writing these exceptions are merely logged, however since it is likely that these exceptions will persist indefinitely something more should be done. One idea is to delete the corrupted contact or event from the remote server.