Update almost all _fired methods to use observe

[aaronayres35]

This PR simply replaces almost all uses of the _fired magically named methods with their observe equivalent.

The only lingering method is here:

pyface/pyface/ui/qt4/dialog.py

Lines 191 to 195 in 6c98a1a

	def _finished_fired(self, result):
	""" Called when the dialog is closed (and nonmodal). """
	self.return_code = _RESULT_MAP[result]
	self.close()

Which I believe will need special care because this is also making use of the qt signal handling

pyface/pyface/ui/qt4/dialog.py

Line 172 in 6c98a1a

dlg.finished.connect(self._finished_fired)

[rahulporuri]

Almost LGTM. Looks like you committed the changes to icons.zip and std.zip files.