Tree view for dashboard

**Is your feature request related to a problem? Please describe.**
On Weblate instances with large number of projects and/or components, clicking through several pages of watched components on the dashboard becomes quite unwieldy.

**Describe the solution you'd like**
A collapsible tree view could make the dashboard more manageable. By default only projects would be shown, with a UI control to expand the components under each project. (NB: there can be several pages' worth of components in a single project.)

**Describe alternatives you've considered**
Alternatively a find-as-you-type search on the dashboard might be useful, but I'm not sure it would be as useful as a tree view.

**Additional context**
https://en.wikipedia.org/wiki/Tree_view