[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.
let's split data and algorithms, this class should contain data fields only and should know nothing about XML and how it is parsed. Let's have another class, or maybe a set of functions that would initialize SignatureData