fix a couple of js urls to send as content-type application/javascript to work with IE nosniff

We started sending 'X-Content-Type-Options: nosniff', but /common/js/templates.js and /test/mocks/site-templates.js were being sent as 'Content-type: text/html; charset=utf-8' and so, not loaded as javascript leading to multiple test failures in the qunit tests.

This changes these to be sent as application/javascript, and while there adds some other missing headers to make these special characters be the same as other single '*.js' files. (Since, in production, these single js files are not sent/referenced, this fix would have no affect in production, but does fix the tests. Or actually, fixes tests, leaving a number of other IE tests broken in current dev branch, which I'll file an issue about in a while).