Appendable original license

[kkkkan]

This is adding feature pull request.

Be able to Add template of original licenses for output html. For example , if add original_license.html file under app directory and add in app's build.gradle like following

licenseTools {
    HashMap<String,String> licensesMap = new HashMap()
    licensesMap.put("The original License","original_license.html")

    originalLicenses=licensesMap
}

and add in licenses.yml like following

- artifact: com.example.original-package:+
  copyrightHolder: You
  license: The original License

, and do generateLicensePage task , generating licenses.html including content of original_license.html .

If you do not set originalLicenses configuration in app's build.gradle and do generateLicensePage task , generated licenses.html is same in generated made by com.cookpad.android.plugin.license-tools v1.2.8.