applets/taskmanager: move "More Actions" item to bottom and rename

Typically menus and toolbars with a "More Actions" item have it at the
end or the bottom of the list of app-specific actions. However the
Task context menu does not do this and has it located at a somewhat
random-seeming location in the middle of the set of items.

This commit moves it to the end of the app-specific menu items and
renames it to "More" to reduce redundancy.