Deprecated slackclient substituted by slack_sdk

Also, some failing tests were corrected.

ugettext_lazy and pytz errors in tests fixed

Some tests failed on django 3, with python 3.8.
Errors were accordingly fixed.

Slack notifications use slack_sdk

The slackclient package has been dprecated and it has now been substituted by the slack_sdk client.

v2.2.14 patch

Patch to fix restart_despooled_tasks management task
substituting non-existing start method with launch.

restart_despooled_tasks

restart_despooled_tasks management task added, in order to manually restart
those tasks in a SPOOLED state, but with no spooler file;
closes #28

v2.2.12

Fix a nasty bug on errors happening duroing emit_notifications, after the task was executed

Bug on comparison of datetimes with dihomogeneous timezones fixed

v2.2.11

Bump version: 2.2.10 → 2.2.11

Fixed bug in next ride computation for monthly periodicity

v2.2.10

Bump version: 2.2.9 → 2.2.10

Fixes Database Error issue

This fixes a DatabaseError stemming from a race condition when saving the report.

Monthly scheduling fixed

This release fixes an error on monthly scheduling causing an infinite loop of task executions.