Remove unneeded sexml code
Rewrite with ningle

Replaces restas with ningle. Restas had 2 problem I could not overcome:
1) It would only let me return a status code or a response, not, for
example, a 403 status code with some json. 2) It would not allow me to
place it under a subdirectory.

Both of these problems possibly (likely) have solutions with restas, but
I already found out how to do these things with ningle.

This rewrite is sloppy and messy. The code should be cleaned up soon.
Use a modal dialog to create tasks

This fixes the issue where focus and input would be lost from the input
field when the story would reload its tasks.

This also makes it a little more uniform with the other forms.
Don't use absolute http://

Apparently it doesn't play nice together with running on https://.
Use *base-directory* to find location of assets

Static assets are located in the `static/' sub-directory of the project.
Locating them with just `static/' works fine if execution is started in
the project's directory, but when starting somewhere else this causes
trouble.
Separate route from function definitions
Fix priorities for tasks

When setting and changing priorities no attention was paid to the
`story_id', which means that no two tasks could have the same priority,
even when belonging to other stories. This creates a weird situation
where the tasks of a certain story would become unmanageable because
there are gaps between the priorities. This could make it seem like
priority changing was impossible.