Feature: calculate arrival time between updates

[qistoph]

The arrival time is currently only refreshed on interval updates.

An interesting idea mentioned in issue #17 is to calculate an up to date arrival time more often.

Thinks to take into account:
(suggestions welcome in comments)

• won't work for commutes with public transport
• maybe directions offers multiple replies for public transport that we can cache for a few minutes

[requiemmg]

If not, you could restrict recalculation to non-public transport commutes.

[irsx02]

For arrival time, is it possible to maybe turn it off? In other words, the screen would just show just the minutes till arrival, and nothing else?
ie. shows this;
[] Home 24 min
instead of
[] Home 24 min 18:24

[radokristof]

When I added this feature I also thought about this, but I think with the current design it is really hard to do this. It would be better to refactor the whole module and process each route individually (so they would update individually) which would enable us to just call a refresh every minute so that the displayed arrival time could be updated.