[Tizen] Bug fix on installing signed widget crash

Originally I will parser node of transform, digital method and digital
hash from signature.xml.  Original parser part causes the crash.  Now
these code will be removed. Because I find there is an API from xmlsec1
library to perform this functionality. Also  signature_types.h will be
removed from repo.

BUG=https://crosswalk-project.org/jira/browse/XWALK-2396
[Tizen] Bug fix on installing invalid widget

The xwalkctl should stop installing invalid widget, Currently there is
no check whether the package is valid package.

BUG=https://crosswalk-project.org/jira/browse/XWALK-2396
Merge pull request #2356 from xuzhang/widgetsignature

[Tizen] Fix two bugs on installing widget