Handlbars comments break the code generation

[ylacaute]

Describe the bug We should be able to add handlebars comments in templates.

To Reproduce Add any comments in a tempalte, for example:

{{!-- Hello --}}

Expected behavior Should be ignored

Context & Motivation As the handlebars templates become quickly unreadable, comments could help a lots.

Your Environment

• 1.29.2
• Debian 8