Revert "Let's not reset our preferences every time we migrate."

This reverts commit f3f2cff.

greatbigcrane/preferences/fixtures/initial_data.json

@@ -0,0 +1 @@
+[{"pk": 1, "model": "preferences.preference", "fields": {"help_text": "Default directory where you store your projects.", "name": "projects_directory", "value": ""}}, {"pk": 2, "model": "preferences.preference", "fields": {"help_text": "Path to execute a terminal on your local system. Use <code>\"#s\"</code> to indicate where to put editor command (for example, <code>xterm -e \"#s\"</code>).", "name": "terminal_path", "value": ""}}, {"pk": 3, "model": "preferences.preference", "fields": {"help_text": "Path to your favourite text editor on your local system. Use <code>open</code> if you're on a Mac.", "name": "editor_path", "value": ""}}]