Add a component for picking the time to send a job

Users need to pick a time in the next 24hrs, or send a file immediately.

Rationale for this is a bit lost in time-before-holiday, but generally:

‘Now’ and ‘later’ as the inital choices makes it really clear what
this feature is about conceptually.

The choice of times is absolute, eg ‘1pm’ not ‘in 3 hours’

tests/app/main/test_choose_time_form.py

@@ -0,0 +1,22 @@
+import pytest
+
+from app.main.forms import ChooseTimeForm
+from freezegun import freeze_time
+
+
+@freeze_time("2016-01-01 11:09:00.061258")
+def test_form_contains_next_24h(app_):
+
+    choices = ChooseTimeForm().scheduled_for.choices
+
+    assert choices[0] == ('', 'Now')
+    assert choices[1] == ('2016-01-01T12:00:00.061258', 'Midday')
+    assert choices[23] == ('2016-01-02T10:00:00.061258', '10am')
+
+    with pytest.raises(IndexError):
+        assert choices[24]
+
+
+@freeze_time("2016-01-01 11:09:00.061258")
+def test_form_defaults_to_now(app_):
+    assert ChooseTimeForm().scheduled_for.data == ''