Add info+ and ace-jump-mode

Add Org speed commands:
- d :: org-todo "DONE"
- y :: org-todo-yesterday "DONE"

Add functions for the agenda:

- Z :: leuven-org-agenda-mark-done-and-add-followup
     Mark the current TODO as done and add another task after it.

- N :: leuven-org-agenda-new
     Create a new note or task at the current agenda item.