Only show widgets on the export dialog that are relevant to the selected
file format (Wave/Ogg):
* Sample rate is always shown.
* Bit depth settings are only shown when Wave is selected.
* Bit rate settings are only shown when Ogg is selected.
Remove the label that informs the user that not all settings apply to
all export formats as it is not needed anymore. The english text of that
label was: "Please note that not all of the parameters above apply for
all file formats."
Remove the rendering logic from the gui code in ExportProjectDialog and let
RenderManger handle it instead.
This is part of an effort to allow the CLI and the GUI to share the same
rendering logic, setting the state for a --render-tracks CLI option similiar to
the "Export Tracks" GUI option.
