No easy way to disable output prompts in HTML templates

[takluyver]

The output_prompt block doesn't do anything in the HTML templates - there's a comment saying:

{# 
  output_prompt doesn't do anything in HTML,
  because there is a prompt div in each output area (see output block)
#}

The output prompts are generated inside the output block for an execute_result output, but there's no easy way (that I can see) to disable them in a subclass template.

[mpacer]

#554 takes care of this! Now you just say --no-prompt :)