Bugfix: Inactive issues marked as "favorite" were logged with 1 minute

- New: You can now add a comment for a booking (part of Jira's API)
- New: You can do quick calculations directly inside the time input, e.g. "5:30 - 1:42"
- Fix: Under certain circumstances, there was an unintended timezone offset when logging timesheets

* Dark mode (follows Jira's theme setting)
* Fixed: Time offset when setting a booking date manually
* Fixed: Recognizes issues with /issues/ URL
* Fixed: Calendar widget cut off visually