Add sourceURL field in PackageInformation (#205)

This field is to be set by the user (or tool?) in the "metadata" section
of the QMSTR yaml config file and it should point to the source of the
package being analyzed

For example:
* http://ftp.gnu.org/gnu/glibc/glibc-ports-2.15.tar.gz
* git://git.myproject.org/MyProject

bom.proto

@@ -10,6 +10,7 @@ message PackageInformation {
 	string ocFossLiaison = 4;
     string ocComplianceContact = 5;
     string licenseDeclared = 6;
+    string sourceURL = 8;
 }
 
 message Person {