Link MEDIA_* settings to file management docs

[Adam Vandenberg]

This patch links the MEDIA_* settings in the full settings list to the "managing files" topic, which has more info on how they are used.

Also tweaks the formatting in those 2 settings, and moves a nearby ref down to where it should go.

[Jannis Leidel]

(In [14533]) Fixed #14524, #14582, #14617, #14665 and #14667 -- Tweaked staticfiles app.

• Updated StaticFilesHandler and AdminMediaHandler to make use of the 404 handler if needed.

• Updated runserver management command to serve static files only in DEBUG mode (or if specified the --insecure option) and if the staticfiles app is in INSTALLED_APPS. Also added an option to disable serving completely (--nostatic).

• Added check in debug mode if STATICFILES_* settings are different to MEDIA_* settings.

• Removed a faulty PendingDeprecationWarning in AdminMediaHandler that is triggered every time runserver is used.

• Fixed an issue with the modification time checks when running collectstatic.

• Extended and refined documentation.

Thanks to everyone for input, especially to Carl Meyer, Ted Kaemming and
Adam Vandenberg for patches.

[Jacob]

Milestone 1.3 deleted