No real changes, just clean up sources by removing trailing spaces from
all the non-generated files.
This should hopefully avoid future commits mixing significant changes
with insignificant whitespace ones.
wxNotificationMessage has been refactored to always use wxNotificationMessageImpl (this was previously already done in the MSW implementation)
This adds various features and fixes to wxNotificationMessage:
- OS X Notification Center implementation
- Generic "toast" notifications
- SetIcon() to specify a custom icon
- AddAction() to add actions to notifications
- Events to get notify of notification clicks, dismiss or actions
