Linkify URLish modal values for event and client data.

This replaces URLs with HTML markup to linkify event
and client values.  This is helpful for specifying client
URLs (metrics, logstreams, etc) and event data (playbook,
relevant metrics, etc).

Screenshot:
https://www.evernote.com/shard/s213/res/f6234bec-c11e-4a48-ab55-6474fd271980