Added a color input widget and updated the code to use that

Please note that this rely on the HTML5 input type="color" which
is only supported in Chrome and Opera. In the future this will be
updated to a custom color picker.
Fixed bug in link hover when the graph was scaled down
Removed hover on links in editor mode
Removed debbuging statements
Fixed hover events in editor on sublinks
Added change event
Added the possibility to add comments on the node.