Replace old-style string formatting with format() method (at least in strings marked for translation)

[seanh]

Some strings in CKAN are passed to gettext with more than one %s in them, this is no good as translators may need to change the order of substituted words.

Strings should not use the old style % substitution, they should use the new format method in Python 2.6+, e.g.:

'This {food} is {adjective}.'.format(food='spam', adjective='absolutely horrible')

​http://docs.python.org/release/2.6.8/tutorial/inputoutput.html#fancier-output-formatting

We should probably only change strings that are marked for translation and that contain multiple %s, don't want to make too much work or cause too many strings to change and need to be re-translated.