Add Unity specific code cleanup rules

[citizenmatt]

Adds a Unity specific code cleanup pattern that reorders file members in the same way as the Default profile, but does not reorder serialised fields. Event functions are grouped before other methods, and sorted so that commonly used/more important functions (such as Update) are listed first. Less commonly used event functions are sorted after, in alphabetical order.

The patterns can be edited and saved to settings, with buttons to populate default, default with regions and empty patterns. The existing file layout settings are not compatible with merging data from a plugin (and "un-merging" if the plugin is disabled/uninstalled), so the Unity patterns are edited and saved separately. A new options page has been added:: Preferences | Languages & Frameworks | Unity Engine | Additional File Layout.