Added metrics for assigned/completed/archived tasks.

Previously, the user page only included open/closed metrics.
Now the results have been differentiated to show the different
types. Additionally, empty cells now show empty instead of 0/0.

Fixes #390
An optimization perhaps?  Use:

```js
Task.find().where({...}).count()
```

This will use the `COUNT` database initiative, which is much faster than looping through the tasks, especially as the tasks grow.  Yes, this will result in 5 queries instead of 1, but the 5 queries should be much much faster.  And the 5 queries can be done in parallel using `async`.