Add support for declassification.

1) Added a new annotation __soaap_declassify(variable)
that allows you to declassify a sandbox private variable
(SOAAP doesn't yet support fields) before it leaks out
of the sandbox, for the cases when this is intended.

2) Added an abstract function  stringifyFact(...) to
InfoFlowAnalysis that aids debugging data flow values
during propagation
Merge branch 'master' of github.com:CTSRD-SOAAP/soaap