reduce serial link logging; clear transmit buffer on disconnect

Another change for issue #3, SerialLink::getCurrentPortS() should now return consistant results on Windows to match linux and OSX

Addition of requestReset to LinkInterface, to allow MavLinkProtocol to detect when connected, but at the wrong baud rate, request a reset.

Changed many functions in the abstract *Link classes to be const. This facilitates setting other functions as const. The metadata for specific links are reset when the links are added.

Changed many functions in the abstract *Link classes to be const. This facilitates setting other functions as const. The metadata for specific links are reset when the links are added.

Changes for new calibration in APM 3.0 (Re: https://github.com/diydrones/MissionPlanner/issues/38), and change in some of the serial timeouts

Modified SerialLink.cc so that it follows the same cross-platform restrictions as the QSerialPort library it relies on.
Windows compilation was broken during 94e91013, which is what prompted this refactoring.

Minor cleanup, fixed a bug where the serial port would not connect on first application launch on Linux

port has to be closed and deleted in the same thread as it was created. changed the disconnect function

Set to 38400,8,N,1 just need to map the baud rate enums now.