Add `LicenseRequired` and `SourceUrl` to package definition

• Add LicenseRequired to Package element as an attribute. Package create will automatically concat all license from files.
  • This field will be used by UIs to show if a package requires a license key.
• Add SourceUrl element to Package element. This will be a link for open sourced projects.
  • This field will be used by UIs to show if a package is opensource.