provide some exception handling block

[marc-portier]

investigate creating a try-except like approach to blocks that should be rendered or hidden as a whole depending on all succeeding

without it we need to surround template sections with exhaustive pro-active testing for possible errors through {% if %} ... {% endif %}

see interesting answer at https://stackoverflow.com/questions/21692387/jinja2-exception-handling#answer-58434921
providing some trick to handle block-like exception handling in jinja2