Fixed missing margins when charts are initially drawn

SWT chart calculates margins only if the plot area has a size bigger
than zero. The size is only calculated once the page is added to the
page book. Hence the "solution" is to update the chart in the #setFocus
method again.
Update statement of assets chart if quotes are updated
Removed dependencies to Java 7
Attached context menu to plot area (otherwise menu is not shown)
Release 0.14.1