More grunt updates:
* Include bbPress version via `package.json` in the 'banner' of minified CSS & JS files
* Include current date and time (UTC) in the 'banner' of minified CSS & JS files
* Props netweb. See #2542



git-svn-id: https://bbpress.svn.wordpress.org/trunk@5333 9866e705-20ec-0310-96e7-cbb4277adcfb
Improve output of `grunt jshint` task. See #2578.

git-svn-id: https://bbpress.svn.wordpress.org/trunk@5334 9866e705-20ec-0310-96e7-cbb4277adcfb
More specific CSS selector on closed topics to only target lists of topics, not single topic views. See r2962.

git-svn-id: https://bbpress.svn.wordpress.org/trunk@5335 9866e705-20ec-0310-96e7-cbb4277adcfb
In `.jshintrc` ignore undefined variables so `grunt jshint` task completes without error.
(reference variables created by WordPress dependencies or API's)
* Props netweb. Fixes #2578



git-svn-id: https://bbpress.svn.wordpress.org/trunk@5336 9866e705-20ec-0310-96e7-cbb4277adcfb