Add Enter Full Screen menu item on OS X

According to the documentation, this should be implemented in apps that
can go fullscreen.
Put the View menu it its customary position

On OS X and GNOME, all apps put File, Edit, View as the first three
items in the menu.  On Windows, the situation is less clear-cut because
of the lack of consistency, but it's similar enough.

Do the same in Poedit, everywhere.
s/__WXMAC__/__WXOSX__/g

The latter is preferred in wx.