App: Enhance descrption of Attribute Fitler URL.

Changes the Attribute Filter URL provided in email and in the
IdP UI to specifically highlight the complete URL required as
opposed to having administrators rely on replacing an ID which
apparently was confusing.

References #52.
Branding: Erronous example.edu.au should be aaf.edu.au
Merge pull request #52 from ausaccessfed/feature/#52-highlight-attr-filter-url

Highlight attribute filter URL in user interface