Dashboard: only show history if it exists

[dotmacro]

Problem

Note: This is very similar to issue #2163

On testing, as soon as the group is created, the dashboard "support %" and "todo %" tabs both correctly indicate that there is no history yet. (This was not tested on live.)

However, on live and testing, as soon as the first distribution period starts, the dashboard "support %" and "todo %" tabs both show 0% for the period preceding the first distribution, even though that period didn't exist -- meaning no users were instructed to send payments, nor could they have marked payments as sent in the app.

Solution

Only show history when history exists. The first distribution period should be the first period tracked on the Support, TODO, and Activity tabs.