Resize synthese.gif to 16x16 pixels

Required so that the graph api's submenu elements in summary page are
all aligned vertically.
Graph plugin: renaming summary graph page

Make name consistent with other graph pages
Graph plugin: improve layout of icons in menu items

Added new CSS with right padding on images to have a small gap between
the icon and the menu text
Graph plugin: improve code to generate plugin's submenus
Whitespace
Graph plugin: align submenus with core summary page
WIP