Add banner image from Wikimania HK
Guard against `Undefined index` errors

Validating checkboxes that were not checked will log a notice for an
Undefined index. Check to see if they are set in array.
Merge pull request #21 from bd808/hklogo

Add banner image from Wikimania HK
Merge pull request #22 from bd808/undefined-data

Guard against `Undefined index` errors