Relative path and command reorg

All node based commands are now relative, e.g.

````
$ cd cms
$ node:move foobar barfoo
$ cd barfoo
$ node:mixin:add . mix:versionable # . is current node
$ cd ..
$ version:checkout barfoo
$ node:prop:set barfoo someprop "Some Value"
$ session:save
$ version:checkin barfoo
$ node:remove barfoo
$ node create /absolute
$ node:create /absolute/path
$ # ...
````