Include Repeat Templates in upcoming(), fixes #122

[bkleinen]

Done. I've decided to do two seperate requests from the api to the database, as upcoming = startdate > today and start=2 has nothing to do with "having a repeat template". the templates store a next instance start date, which I don't use, as they are always in the future.

I've extracted some of the date query logic in order to provide a fixed date for "today" from the tests.

I've added two tests that show the (imho incorrect) behaviour on cancelled/completed tasks: test_upcoming_includes_completed_and_canceled

this is because the test data has a incorrect start value:
test_upcoming_includes_repeating_instance

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[bkleinen]

Having slept over this, I realized that I would like / it needs a third option for the parameter, so not only this:

tasks = things.tasks(is_repeating_task_template=True)
tasks = things.tasks(is_repeating_task_template=False) #default, as this is set in the current version

but also this:

tasks = things.tasks(is_repeating_task_template=None)

because I would want to be able to ask for tomorrow's tasks with the repeats.

As my branch name was incorrect anyways I close this PR and will open a new one (or re-open this one, if you prefer?) when done.