Update slapos.recipe.template key (url, inline, output)

I'm working on replacing slapos.recipe.template and slapos.recipe.template:jinja2 to harmonize the option keys (url, inline, output).

Here is the test suite for python 2 and for python 3

For Python 3, I think it's fine. But for Python 2, I have a problem with Caddy-Frontend, I have an error with the promise checking information (I think the "inline" option is interpreted differently than the "template = inline:" option).

I will try to modify the Caddy-Frontend files in steps to update the option names.