Added Configuring Default Applications doc and media.

content/en/managing-your-system/configuring-default-applications.md

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+## Configuring Default Applications
+
+You can configure default applications by going to the Budgie Menu, opening Settings app, and going to the Details section.
+
+Upon entering the Details section, go to Default Applications.
+
+![Default Applications](../../images/managing-your-system/settings-default-applications.png)
+*Note: In the image above, we've changed the Music player and Video player.*
+
+You can change default applications for:
+
+- Calendar
+- Mail client
+- Music player
+- Photo viewer
+- Video player
+- Web browser