Added a request history panel to the debug toolbar for easier Ajax debug

[NyanKiyoshi]

Hello!

This is a little edit that I think quite useful to debug and profile Ajax requests that I think could be useful to Saleor to have.

This PR adds a new panel to django-debug-toolbar which tracks the request history and kept the list updated, allowing us to to gain an easy access to Ajax requests.

Screenshots

Request list made on dashboard 2.0

SQL requests made on dashboard 2.0 on an Ajax request

Pull Request Checklist

1. Privileged views and APIs are guarded by proper permission checks.
2. All visible strings are translated with proper context.
3. All data-formatting is locale-aware (dates, numbers, and so on).
4. Database queries are optimized and the number of queries is constant.
5. The changes are tested.
6. The code is documented (docstrings, project documentation).

[codecov]

Codecov Report

Merging #2271 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2271   +/-   ##
=======================================
  Coverage   87.32%   87.32%           
=======================================
  Files         176      176           
  Lines        7872     7872           
  Branches      810      810           
=======================================
  Hits         6874     6874           
  Misses        756      756           
  Partials      242      242

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