Add workaround for outline-mode bug

Altered items:
simple-call-tree-set-attribute
New commands & keybindings simple-call-tree-up/down-priority

New options: simple-call-tree-org-highest-priority
             simple-call-tree-org-lowest-priority
Also rename simple-call-tree-org-todo-states to simple-call-tree-org-todo-keywords

Altered items:
simple-call-tree-org-highest-priority,
simple-call-tree-org-lowest-priority,
simple-call-tree-org-todo-states, simple-call-tree-org-todo-keywords,
simple-call-tree-mode, simple-call-tree-set-todo,
simple-call-tree-next-todo, simple-call-tree-prev-todo,
simple-call-tree-set-priority, simple-call-tree-up-priority,
simple-call-tree-down-priority