Tk: added missing config vars and tests

Added two variables tkhorsize & tkvertsize
to config2.py and added new test file in tests/tk_tests.py
with tests for Tkinter and Tkdialog and disabled them on Travis.

Bug: T75025
Change-Id: I51545f8f1a3e841bcfc6fe9b1da90f4265770725
Merge "Tk: added missing config vars and tests"