grunt: Add jsonlint

Change-Id: Icace398eef40556a3fd4865cb763043c086da469
grunt: Update watch file patterns

* ".jscs.json" doesn't exist anymore (was renamed to ".jscsrc").
* ".csslintrc" doesn't exist.
* Use "jscs.all" instead of jshint.all as the latter doesn't have
  the jshintignore pattern applied (no need to monitor the deep
  node_modules/ directory structure with lots of file stats)
* Add "jsonlint.all".

Change-Id: Ie9d681b7c4a6424c069f258774be46d44f6386e9