use `placeholder` instead of `value` in html5 - editor.mako
whitespace
Merged in trevorw/galaxy-central (pull request #331)

whitespace
Merged in trevorw/galaxy-central-1//use-placeholder-instead-of-value-in-html-1392839097891 (pull request #325)

use `placeholder` instead of `value` in html5 - editor.mako