External api for OMIM from disease page

This is still in a rough state. It gets only the OMIM title through API for OMIMs tags within tgenes_by_biology table and genes_by_orthology table of a Disease page. A short title is displayed by the OMIM ID, in parenthesis. 

A sample disease page: ``resources/disease/DOID:0050432#012--10``

**To test locally you will need to copy the API key** from ``/home/sgao/wb/website/credentials/omim_apikey.txt ``to your ``credentials/`` directory at the root of ``website/``

**In case of external resource is unavailable** (to simulate an error, uncomment the ``die`` statement inside ``sub _omim_external`` in ``WormBase::API::Role::ThirdParty::OMIM;``) 
- The table will display normally, except that the short title will be missing
- The widget with missing information will not be cached

**limiting number of requests to external resources**
- Will stop making requests for 10min, if an error response is received (refer to t/api_test/disease.t)
- Has **Not** implemented the upper limit on number of OMIM entries per request, because we are only requesting OMIM titles, which OMIM doesn't have a upper limit per request. 

@acabunoc I think it's ready to be reviewed
I don't want the 'error' key to show up in the hash at all, if there's no error.