#20 Allow to select which days get totalled

[Tor Bjornrud]

Allow the user to select which days get added to the total.

For instance, my pay lags behind by two weeks. By the
time I get paid, I forgot how many hours I've worked on
something, and would like to ballpark about what I'm
going to make.

As it stands, there is no way to highlight a block of
days (in this instance, a two week block) and then hit
total.

It would be nice if you could just drag the stylus over
the block and hit total.