I can add tasks quickly without waiting for page refresh

- Only submit. No "Submit and continue" covered yet.

- Can reuse most of the information used by update in overlay:
-- get-card json (type of card missing)

The main difference with update overlay will be that we need to create a brand new card in JS.
The proposal is to create it based on the json return instead of creating it in HTML on the server. It was not possible for update in card because update needed to know if we were updating a task/bug/testcase (in yellow) or a story (in gray). It's not a problem with creation as we only manipulate "tasks" (or bugs/testcases,etc)