Tree view for dashboard

[tjhietala]

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

[nijel]

Possibly related to #263