Fixed grunt errors, added telemetry json to gitignore file

Fixes

1. When copying files for telemetry, CSS directories were not flattened. Hence the CSS files were not copied
2. Added telemetry json files to .gitignore as they are not checked in
3. The file `node_modules/topcoat-checkbox/test/perf/checkbox-test.jade` does not exist, so removing that special case.