More work to unify the tab view with the overall
UI look-and-feel, allowing you to remove and add
tabs via mouse over rather than the close tab
icon. Also added a number of cosmetic adjustments.
Fixed up PerformanceManager and ScatterPlot to
pick up on the chart fonts and tick size etc.
Removed some erroneous static members in the
ScatterPlot that caused a SEGV when adding multiple
charts (or cancelling an add then adding again).