Update Debian package to run Dogtail using Python 3

Originally created by @anonym on #12185 (Redmine)

Currently we install python-dogtail, which uses Python 2 and makes it impossible to deal with objects containing unicode character (e.g. “Save As…” (note the triple dots)).

The Debian packaging repo for dogtail has switched to Python 3 since almost a year back, but there has been no release since then. However, I tried building a package and installing it, and it worked fine vs unicode strings at least.

Part of the “Make test suite survive tech changes” roadmap item.

Related issues

• Blocked by #14585 (closed)
• Blocks #15953 (closed)
• Blocks #16976 (closed)