Tk: Migrated Tkdialog class to gui.py

Migrated Tkdialog class from scripts/flickrripper.py to
pywikibot/userinterfaces/gui.py Added packages dependencies in setup.py
and tests/scripts_tests.py. Added test to tests/tk_tests.py

Bug: T78505
Change-Id: I0001ec541f2b6679354314b92331f0cfcd381383
Merge "Tk: Migrated Tkdialog class to gui.py"