[Tizen] Add signature data and parser logic

SignatureFile: according to widget spec, widget should includes
signature file in the zip. SignatureFile is used to label signature
files in the widget. There are two types of signature files: author
and distributor signature.

SignatueData: it is used to store values parsing from signature.xml.
The data will be used by signature verifier to validate digital
signatures.
but you've a public setter for 'transform_algorithm_' , so far I do not see how this class is better than simply
struct ReferenceData  {
std::string transform_algorithm;
....
};