feat(tags): allow to forcefully replace an existing tag

[keplicz]

This patch adds a "Replace an existing tag" checkbox to the New Tag dialog.

Currently moving a tag from one commit to another needs two separate interactions to delete and then create a new tag. This proposed patch allows to control force=True of Repository.create_reference().

[jorio]

Hi, thank you for your contribution! Sorry for my belated feedback.

1. Please recreate ui_newtagdialog.py with ./update_resources.py --ui to ensure compatibility with all Qt bindings and our localization system. (If it doesn't do anything, try deleting ui_newtagdialog.py first)
2. Can you add a unit test for the new feature? You can basically duplicate testNewTag and tweak it a bit to overwrite the existing tag named annotated_tag.

Thank you!