Add ApiFlowViewTopicList

Adds a new API module, similar to the existing ones, to request a
a list of topics.

Note that I'm including 'render' as submodule-parameter.
The better way would be to make use of the 'render' param in ApiFlow.php,
but this server-side rendering will go away anyway.
Figure it's better to keep it as-is for now, and just get rid of it
altogether once client-side rendering is in place.

Change-Id: I659687cbd1563ced0a5e9d7ae9514a62b0b43474