Centralize all connecting and disconnecting of links through
LinkManager::[Connect|Disconnect]Link api. Connect/Disconnect no longer
allowed through LinkInterface. This allows creation of new
LinkManager::setConnections[Suspended|Allowed] methods to disallow
connections as needed.

This is the Pixhawk research board, not the PX4 production board.

This api doesn’t make any sense given the fact that LinkInterface
signals bytesReceived with the bytes in the signal. Also the reason why
it is never called!

Converted LinkInterface from a pure-virtual interface into an abstract base class. This centralized the data rate calculation code for all subclasses. Also added the necessary code to provide upstream/downstream data rate calculations for all LinkInterface-derived classes.

Renamed getNominalDataRate to getConnectionSpeed. Also added upstream/downstream data rate functions to all Link classes.

Removed LinkInterface methods which were never being called. Updated various LinkInterface implementation classes to remove the methods. Some methods such as the ones which measure data rates or bits sent/received were implemented in only some of the implementation classes, and in some cases implemented incorrectly. If they were called, the values returned would be incorrect. Although there was some partial implementation for these I removed them as well since in all case they were never being called by any code. In checking Blame, these came across in 2010 and have remained unimplemented since them, so I figure better to clean up than leave crufty, unused, half finished stuff in.

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.

Changed NUM_OUTPUT_SIGNALS to an const unsigned short from a #define and moved its definition into OpalRT.h from OpalLink.h so that the configuration would all be in one place.

OpalLink should now be able to be disconnected.  I also added a test to see if params had already been allocated before calling new in OpalLink::connect()

Cleaned up communication structure significantly, should now be easier to add new links. Signal bytesReceived(link, QByteArray) is now only way to pass on newly received data