Sets sames margin sides for graphs in a same zone

Adds button on plot overlay to show/hide x-axis properties

Shows/hides plot overlay when entering/leaving graph

Calls 'close graph' action when selecting close item in overlay

Adds title and close items in plot overlay

Passes directly GraphWidget in delegate It will allow to get title and call close action in plot overlay

Removes title and close button from graph widget Title and button will be added directly as items in plot overlay

Removes margins from visualization widgets

Merge branch 'feature/NbPointsColumn' into develop

Adds column to display nb points in variable widget