WPF: Several bug fixes with fonts, loop cells and wave form rendering.

- Fixed several bugs with using custom resource fonts in XAML style
classes, custom control classes with programatically set font families,
and using the right font family and typeface in GraphicsContextWrapper.
- The wave form control is no longer rendering out of bounds.
- The loop name textbox is now closed when selecting another row, when
selecting another column.
- Fixed bubbling of double click and single click inside the loop name
text box (i.e. double clicking or pressing enter inside the text box
doesn't start/stop a loop anymore).