Implement watch command

This allows you to continously monitor all the child watches that, recursively,
fire under <path>.

Examples:

(CONNECTED) /> watch start /
(CONNECTED) /> create /foo 'test'
(CONNECTED) /> create /bar/foo 'test'
(CONNECTED) /> rm /bar/foo
(CONNECTED) /> watch stats /

Watches Stats

/foo: 1
/bar: 2
/: 1
(CONNECTED) /> watch stop /