Renaming WordsToAvoidHighlighter

we want to provide guidance on words to avoid,
which is done by highlighting those words on
browsers where it is supoported, and by other
means^ where highlighting is not supported

^ TBD
Words to avoid feature cross-broswer compatibility

on IE8 and below we will disable highlighting
but retain the alert box on the right.

whereas, on all other browsers we will enable
alerting as well as highlighting.
Optimised way to find  words to avoid used

if highlighting works we don't need a text
search to find words to avoid being used.
Making list of words to avoid DRY
Merge pull request #1406 from alphagov/words-to-avoid-cross-browser-compatible

Words to avoid cross browser compatible