fix handling of conflicting actions from tools

when a tool gets activated, all of its actions are enabled by
the tool manager. if there is already an action with the same
shortcut/name (for instance a standard action like select all),
then these action will conflict. this means their shortcut will
not work. thos patch disables the existing conflicting action
when activating the tools actions, and re-enables them when the
tool get deactivated. this way tools can "overload" existing
actions if they get assigned the same name.