Action Button: use getFont() to calculate text position rather than default FONT

Conflicts:

	applications/plugins/org.csstudio.swt.widgets/src/org/csstudio/swt/widgets/figures/ActionButtonFigure.java
Action Button: call calculateTextPosition() whenever text or font changes, and when width or height changes, get the corresponding value from the prop sheet rather than the widget
Merge pull request #669 from dls-controls/action_button_font

Action button font