Only load drafts in CodeMirrorDemo for signed in users

Drafts are not supported for anonymous users, as there is no way to
identify them and keep the draft private.  Only call the drafts() API
to load drafts if the user is signed in, and only support the "c"
keybindings if the user is signed in.

Change-Id: I8eedc8bd8e18f2c379b362f1f0cad9c85ed508a5
1 file changed