convert custom attributes to validation-friendly format

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standard Wagn pages don't validate as proper HTML, in part because they contain custom attributes (eg card-id here: <div card-id="123">).

use attributes that begin with the prefix "data-". this validates.

I started down this road with slot attributes (now in master). this probably wouldn't be a huge challenge.

--Ethan McCutchen.....2013-08-20 21:14:52 +0000

note: this introduced a rule-editing bug. patched / deploying.

--Ethan McCutchen.....2013-09-03 17:33:19 +0000

HTML on new wagns is completely valid.

--Ethan McCutchen.....2013-09-10 19:48:17 +0000