Fix auto gain + sea state
Widen radar blobs when scanlines have been missed.

The radar has 2048 possible scanlines that it can transmit.
The 4G usually transmits about half that per revolution.
The BR24 transmits between half and one third per revolution.

A new (default) drawing algorithm widens the blobs drawn when the previous scanline(s) are not transmitted.
The previous drawing algorithm can be used by editing the opencpn.ini and setting DrawAlgorithm=0 instead of DrawAlgorithm=1.
Rotate received spokes at heading at time of reception.

Douwe pointed out that if the boat rotates whilst the radar spokes are received they are drawn at the wrong rotation.
We now keep a heading stored with the spoke, and always draw relative to that. This reduces the 'rotation error' from
2,5s to 1s, or more if old spokes are shown.