This commit allows the option `-a|--alias` for `grit add` that will
allow aliasing a node on addition.

`grit list` will now recognize "all" as a special selector, listing
*all* nodes including children nodes.

Add new "move" command that allows a node to be moved from one parent to
another.

It simply aliases the action of unlink a node and re-linking it with a
different parent.

The options allow unlinking a node from all children or all parents,
these options are mutually exclusive (including the existing "target"
arguemnts)

The app crashes if no node for the current day has been created, either
from `add` or something else. This allows the user to specify `today` as
a keyword in order to automatically add the date node.

`grit tree -u` will sort the nodes by order of Inactive -> InProgress ->
Completed. This is helpful in seeing what needs to be done still.