Update django-tables2 to 1.7.0

[pyup-bot]

There's a new version of django-tables2 available.
You are currently using 1.6.1. I have updated it to 1.7.0

These links might come in handy: PyPI | Changelog | Repo

Changelog

1.7.0

• Make title() lazy (443 by ygwain, fixes 438)
• Fix __all__ by populating them with the names of the items to export instead of the items themself.
• Allow adding extra columns to an instance using the extra_columns argument. Fixes 403, 70
• Added a hook before_render to allow last-minute changes to the table before rendering.
• Added BoundColumns.show() and BoundColumns.hide() to show/hide columns on an instance of a Table.
• Use <listlike>.verbose_name/.verbose_name_plural if it exists to name the items in the list. (fixes 166)

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖