Add skill filter to task list page

# Problem

On the task list page, we should have the option to filter by skills.


Clicking on the filter shows a dropdown


The dropdown contains the user's own skills in the first grouping, with other skills in the second grouping. **Possibly these could be project skills or a union of all current task skills?** I guess that part depends on how the filter is implemented - client or API side.

When a filter is applied, we show which filters are active as a list of "dismissible" buttons.