Secrecy on user input

[alevy]

1. Allow annotations in HTML as to how the data will be labeled
2. Extend LBson to allow for Labeled (Labeled Bson.Document) types -- this will effectively allow for the insertion of data more secret than the clearance (but not really since the outer label will have to be below clearance). Interestingly, this will allow for the insertion of data that a policy specifier cannot declassify and thus exfiltrate