Support Django 2.2 & Django Debug toolbar 2.2 and above

[mintusah25]

The current codebase master branch is still using the old Django feature that has removed in 2.2. Also, middleware is not compatible with Debug toolbar.

[martin-thoma]

  File "/usr/local/lib/python3.8/site-packages/debug_panel/middleware.py", line 7, in <module>
    from django.core.urlresolvers import reverse, resolve, Resolver404
ModuleNotFoundError: No module named 'django.core.urlresolvers'