Allow extensions to contribute to project filter

[dcoraboeuf]

In the home page, one can filter projects by name. But extensions should be able to provide their own search criteria, by displaying a search text or combo, and by using it to filter further on the projects.

The filter would be persisted locally and/or associated with a permalink.

The filter is applied on the server and the home page must be adapted to call an end point which includes the filters and their configuration.

The name filter is kept as-is, on client side.