Show list of notes as links on the side menu

Show the notes and directories that are one level deep.
Adjusted the css related to the menu, such that it flows
well.
Fix: Ensure save requests are valid

Navigating quickly between notes caused
invalid save requests to be made, using
data from a previous page.
Add 'back' icon

Add an icon to the menu for going up one level
in the notes heirarchy.