Add endtime to event model

[johan-bjareholt]

We currently have an issue when fetching events by starttime and endtime.

23:00                             00:00                           01:00
<----------------------------------------------------------------------
         | event start                                 event end |

If we have a case like this and we have an event which starts before 00:00 and ends after 00:00, if we query with startime=the_second_day we will not get the event even though it is within the second day.

Currently we are checking the datetimes like this

if event.starttime >= starttime and event.starttime <= endtime:
    return event

What we actually should do when fetching events with a starttime and endtime

if event.endtime >= starttime and event.starttime <= endtime:
    return event

This would however require us to add a "endtime" field to save in every datastore.
At that point we could also remove the duration field since it's essentially endtime-starttime to save on db size.

TL;DR: Our datastorages cannot filter by starttime+duration to get the endtime, we need an actual endtime field instead of duration to be able to filter after endtime and fix a few quirks when having events in between two dates.

[ErikBjare]

I'm aware of this issue, and this is certainly a clear way to fix it but would require quite a lot of work to get done.

If we were to implement this, we'd do it in together with the other changes suggested in ActivityWatch/activitywatch#109

[ErikBjare]

There might be a way to do this for the SQLite datastore by either using a view or something else that computes endtime (and makes it queryable) from timestamp and duration. Will have to investigate, but might not even require a database migration, so that would be cool.