File class members are encapsulated, and internal lock was added.

A lock was added to the file class to properly handle multiple threads accessing the self encryptor. Actual chunk storage and incrementing is still a work in progress.

This technically completes JIRA ticket MAID-153 too.
This will be interesting because I think these are only enforced when the self_encryptor is closed. Its one of my many concerns - I think we may have to force flush large files to disk (or something!). I will test this today.