Changed densenet-tf models to tf2

[Anna-Mironova]

TODO:

• Add APACHE-2.0-TensorFlow.txt

[eaidova]

@IRDonch do you know, why windows demo build failed?

17:16:30    File "C:\jenkins\workspace\omz\precommit\demos_windows10\venv\lib\site-packages\numpy\__init__.py", line 302, in _win_os_check
17:16:30      raise RuntimeError(msg.format(__file__)) from None
17:16:30  RuntimeError: The current Numpy installation ('C:\\jenkins\\workspace\\omz\\precommit\\demos_windows10\\venv\\lib\\site-packages\\numpy\\__init__.py') fails to pass a sanity check due to a bug in the windows runtime. See this issue for more information: https://tinyurl.com/y3dm3h86
17:16:30  CMake Error at CMakeLists.txt:191 (message):
17:16:30    NumPy headers not found

[IRDonch]

@eaidova See #1923.