Show the size of pipeline in the project manager dashboard

[laurentS]

In order to keep an eye on how much work is available in the project pipeline, it could be helpful to add a couple of simple metrics to the admin dashboard:

• number of projects available to map
• area lined up to map (in km2)
• estimated hours/days of mapping (for instance, assuming 1s/task avg speed)

These could be very roughly estimated (the numbers will be wrong anyway, so we just want some simple value) from the area of each project, or requiredResults, so that there is no extra data to store/pass around, and the calculation can be quickly done in the dashboard itself.