Support the imports header property

[yuv01]

What would you like to be added?

Add support for the header's imports property.

Why is this needed?

Instead of managing a one large .mw file, each project directory could have its own file with minimal tasks.
Then at the root level or wherever, you can have a main .mw file which handle imports of the relevant projects and gives an overall view with everything you need.
The group\section name could have a link to the small .mw file so when clicking on it you can go to the project's page.