History panel: allow more content types (e.g. Excel spreadsheet)

[raphaelmerx]

Description

The Debug Toolbar history pannel is very useful for AJAZ json requests. Unfortunately, it doesn't work for non-ajax, non-json requests - for example, a "Download data" button that downloads an Excel file generated on the fly. It would be great to tweak that, potentially through a configuration option.

Example implementation

• Add a configuration option CAPTURED_CONTENT_TYPES, defaults to ["application/json"]
• Can be extended in the settings
• In middleware.py:

            if request.is_ajax() or content_type in self.config["CAPTURED_CONTENT_TYPES"]:
                toolbar.render_toolbar()

[tim-schilling]

The call to is_ajax was removed in #1382 which allows the toolbar to instrument almost all requests. The types of responses that aren't allowed are visible here.

That PR hasn't been included in a released version yet, so if you need it immediately you'll need to install from source.

[tim-schilling]

Actually, I think the toolbar instruments all requests with 1382 now.