Add new rule for detecting CSS comments

[scripthunter7]

e.g.

#$#body { padding: 0; /* foo */ }
##.ad /* bar */

Suggested rule name: no-css-comments

Can be autofixed

Note:

By default, AGTree is tolerant and will parse these rules. However, we should throw an error for such rules.

Additionally, the extension will discard them too.