Site-level preferences are located in TWikiPreferences, however this TWikiPreferences prefs topic has override priority and should be used for local customizations. This allows for easier upgrades as you don't need to worry about the shipped preferences clobbering yours. It's easier to keep a handle on if you only copy over the settings you actually change.
Quick edit of existing preferences (edit the topic text to set new preferences)
Site Specific Site-wide Preferences
Editor for ACTIONTRACKERPLUGIN
Set ACTIONTRACKERPLUGIN_USENEWWINDOW = 0
Set ACTIONTRACKERPLUGIN_EDITHEADER = | Due date | State |
Set ACTIONTRACKERPLUGIN_EDITFORMAT = | $due | $state |
Set ACTIONTRACKERPLUGIN_EDITORIENT = cols
Set ACTIONTRACKERPLUGIN_TABLEHEADER = | Due date | Description | State ||