Fix sampler rate control setup in DlgPrefControls.
Check that enabled CO is not null, which it can be during shutdown.
Fix incorrect signal/slot connection
Ensure that vinyl control decks 3 and 4 can be enabled if they exist
Merge pull request #132 from ywwg/vinyl-menu-fixes

Ensure that vinyl control decks 3 and 4 can be enabled if they exist
If there are no playing decks and follower is enabled, reset bpm as well as beat distance
Add QProperty to WPushButton for whether the widget is pressed.
Add QProperty to WWidget for the widget value and disabled state.
Add <Text> node for each WPushButton <State>. Allows push-buttons without pixmaps.
Link MIDI input/output ports that have have "in" in the input port and "out" in the output port.
Allow WPushButton to be styled with a style sheet.
Allow WSliderComposed to be styled with a style sheet.
Allow WStatusLight, WDisplay and WKnob to be styled with a style sheet.
Remove duplicate method.