Find existing card by bugIdFieldName if possible

Modify findCardByName() to findCardByNameOrBugId(), which checks for
existing Mingle card by bugIdFieldName if there is one.
This fixes issue #18.

Also add informative bingle.info output, and add a TODO for Mingle card name.
Merge pull request #20 from skierpage/checkBugIdField

Find existing card by bugIdFieldName if possible