Shimmer Bluetooth driver updates

Allow baudrate to be set to 230400 using preprocessor definition: USE_230400_BAUD
Remove dependency on shimmerMessage.h for sending packets (as was needlessly inefficient for this purpose). Almost doubles max permissible outgoing packet size to 255 bytes.
Shimmer gyro driver update

Default SER0_CTS signal to give gyro signals and no longer modify when starting or stopping (allow higher level app do this as necessary)