ENH: Added SerialDevice base class

Makes it easier to add serial port devices by:
	- searching for appropriate port on any platform
	- calling to test whether the device is present and talking
(override isAwake() method)
	- close the port when device garbage collected
	- send commands and receive responses more easily

also updated changelog
Merge pull request #654 from jeremygray/master

BF: appData.cfg was growing without bounds; closes #649
FF: need a wx.App for localization (e.g., for gui.py)