defaultpropertyeditor: remove double-underscore identifiers

ui.timelinecanvas: remove double-underscore identifiers

mainwindow: remove double-underscore identifiers

webcam_managerdialog: remove double-underscore identifiers

ui.timeline: remove double-underscore identifiers

zoominterface: remove double-underscore identifiers

ui.preview: remove double-underscore identifiers

ui.projecttabs: remove double-underscore identifiers

ui.propertyeditor: remove double-underscore identifiers

previewer: remove double-underscore identifiers