Fix template debug warning on Category page

[duker33]

Category page contains several debug warnings:

• at h1
• at text
• at product siblings list

To enable template debug warnings put this code to your settings/local.py:

DEBUG = True

# to debug templates: https://stackoverflow.com/questions/8990224/make-django-templates-strict
TEMPLATES = [
    {
        **TEMPLATES[0],
        'OPTIONS': {
            **TEMPLATES[0]['OPTIONS'],
            'string_if_invalid': 'DEBUG WARNING: undefined template variable [%s] not found',
        }
    }
]